procfs task exe symlink

The kernel implements readlink of /proc/pid/exe by getting the file from
the first executable VMA.  Then the path to the file is reconstructed and
reported as the result.

Because of the VMA walk the code is slightly different on nommu systems.
This patch avoids separate /proc/pid/exe code on nommu systems.  Instead of
walking the VMAs to find the first executable file-backed VMA we store a
reference to the exec'd file in the mm_struct.

That reference would prevent the filesystem holding the executable file
from being unmounted even after unmapping the VMAs.  So we track the number
of VM_EXECUTABLE VMAs and drop the new reference when the last one is
unmapped.  This avoids pinning the mounted filesystem.

[akpm@linux-foundation.org: improve comments]
[yamamoto@valinux.co.jp: fix dup_mmap]
Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: David Howells <dhowells@redhat.com>
Cc:"Eric W. Biederman" <ebiederm@xmission.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
index c12cc362fd3bc2a230716810c9edab2552335512..3b40d45a3a16501ca0ea28563b8049c6e3718698 100644 (file)
--- a/fs/binfmt_flat.c
+++ b/fs/binfmt_flat.c
@@ -531,7 +531,8 @@ static int load_flat_file(struct linux_binprm * bprm,
                DBG_FLT("BINFMT_FLAT: ROM mapping of file (we hope)\n");
 
                down_write(&current->mm->mmap_sem);
-               textpos = do_mmap(bprm->file, 0, text_len, PROT_READ|PROT_EXEC, MAP_PRIVATE, 0);
+               textpos = do_mmap(bprm->file, 0, text_len, PROT_READ|PROT_EXEC,
+                                 MAP_PRIVATE|MAP_EXECUTABLE, 0);
                up_write(&current->mm->mmap_sem);
                if (!textpos  || textpos >= (unsigned long) -4096) {
                        if (!textpos)

diff --git a/fs/exec.c b/fs/exec.c
index 711bc45d789c54886d1836ab0845b10bd7884714..a13883903ee98587951681e143c36d9712460515 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -964,6 +964,8 @@ int flush_old_exec(struct linux_binprm * bprm)
        if (retval)
                goto out;
 
+       set_mm_exe_file(bprm->mm, bprm->file);
+
        /*
         * Release all of the old mmap stuff
         */

diff --git a/fs/proc/base.c b/fs/proc/base.c
index c5e412a00b170e5294964505726b85f6cff93309..b48ddb1199459530560a35cfeda4271cda3698b2 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1181,6 +1181,81 @@ static const struct file_operations proc_pid_sched_operations = {
 
 #endif
 
+/*
+ * We added or removed a vma mapping the executable. The vmas are only mapped
+ * during exec and are not mapped with the mmap system call.
+ * Callers must hold down_write() on the mm's mmap_sem for these
+ */
+void added_exe_file_vma(struct mm_struct *mm)
+{
+       mm->num_exe_file_vmas++;
+}
+
+void removed_exe_file_vma(struct mm_struct *mm)
+{
+       mm->num_exe_file_vmas--;
+       if ((mm->num_exe_file_vmas == 0) && mm->exe_file){
+               fput(mm->exe_file);
+               mm->exe_file = NULL;
+       }
+
+}
+
+void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
+{
+       if (new_exe_file)
+               get_file(new_exe_file);
+       if (mm->exe_file)
+               fput(mm->exe_file);
+       mm->exe_file = new_exe_file;
+       mm->num_exe_file_vmas = 0;
+}
+
+struct file *get_mm_exe_file(struct mm_struct *mm)
+{
+       struct file *exe_file;
+
+       /* We need mmap_sem to protect against races with removal of
+        * VM_EXECUTABLE vmas */
+       down_read(&mm->mmap_sem);
+       exe_file = mm->exe_file;
+       if (exe_file)
+               get_file(exe_file);
+       up_read(&mm->mmap_sem);
+       return exe_file;
+}
+
+void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
+{
+       /* It's safe to write the exe_file pointer without exe_file_lock because
+        * this is called during fork when the task is not yet in /proc */
+       newmm->exe_file = get_mm_exe_file(oldmm);
+}
+
+static int proc_exe_link(struct inode *inode, struct path *exe_path)
+{
+       struct task_struct *task;
+       struct mm_struct *mm;
+       struct file *exe_file;
+
+       task = get_proc_task(inode);
+       if (!task)
+               return -ENOENT;
+       mm = get_task_mm(task);
+       put_task_struct(task);
+       if (!mm)
+               return -ENOENT;
+       exe_file = get_mm_exe_file(mm);
+       mmput(mm);
+       if (exe_file) {
+               *exe_path = exe_file->f_path;
+               path_get(&exe_file->f_path);
+               fput(exe_file);
+               return 0;
+       } else
+               return -ENOENT;
+}
+
 static void *proc_pid_follow_link(struct dentry *dentry, struct nameidata *nd)
 {
        struct inode *inode = dentry->d_inode;

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index bc72f5c8c47d34704cb6a76ef450e1bd6dc84f0d..45abb980398830959110404b6a9181e957c5953d 100644 (file)
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -48,7 +48,6 @@ extern int maps_protect;
 
 extern void create_seq_entry(char *name, mode_t mode,
                                const struct file_operations *f);
-extern int proc_exe_link(struct inode *, struct path *);
 extern int proc_tid_stat(struct seq_file *m, struct pid_namespace *ns,
                                struct pid *pid, struct task_struct *task);
 extern int proc_tgid_stat(struct seq_file *m, struct pid_namespace *ns,

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 7415eeb7cc3a75dda762e78052e49a77f6a509ff..e2b8e769f510d676997698b8fd28ef4346478d2c 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -75,40 +75,6 @@ int task_statm(struct mm_struct *mm, int *shared, int *text,
        return mm->total_vm;
 }
 
-int proc_exe_link(struct inode *inode, struct path *path)
-{
-       struct vm_area_struct * vma;
-       int result = -ENOENT;
-       struct task_struct *task = get_proc_task(inode);
-       struct mm_struct * mm = NULL;
-
-       if (task) {
-               mm = get_task_mm(task);
-               put_task_struct(task);
-       }
-       if (!mm)
-               goto out;
-       down_read(&mm->mmap_sem);
-
-       vma = mm->mmap;
-       while (vma) {
-               if ((vma->vm_flags & VM_EXECUTABLE) && vma->vm_file)
-                       break;
-               vma = vma->vm_next;
-       }
-
-       if (vma) {
-               *path = vma->vm_file->f_path;
-               path_get(&vma->vm_file->f_path);
-               result = 0;
-       }
-
-       up_read(&mm->mmap_sem);
-       mmput(mm);
-out:
-       return result;
-}
-
 static void pad_len_spaces(struct seq_file *m, int len)
 {
        len = 25 + sizeof(void*) * 6 - len;

diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index 8011528518bd7e73d022498466e79257bd2695ec..4b733f108455273ce52ce73c4f410d74a9ea2b2e 100644 (file)
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -103,40 +103,6 @@ int task_statm(struct mm_struct *mm, int *shared, int *text,
        return size;
 }
 
-int proc_exe_link(struct inode *inode, struct path *path)
-{
-       struct vm_list_struct *vml;
-       struct vm_area_struct *vma;
-       struct task_struct *task = get_proc_task(inode);
-       struct mm_struct *mm = get_task_mm(task);
-       int result = -ENOENT;
-
-       if (!mm)
-               goto out;
-       down_read(&mm->mmap_sem);
-
-       vml = mm->context.vmlist;
-       vma = NULL;
-       while (vml) {
-               if ((vml->vma->vm_flags & VM_EXECUTABLE) && vml->vma->vm_file) {
-                       vma = vml->vma;
-                       break;
-               }
-               vml = vml->next;
-       }
-
-       if (vma) {
-               *path = vma->vm_file->f_path;
-               path_get(&vma->vm_file->f_path);
-               result = 0;
-       }
-
-       up_read(&mm->mmap_sem);
-       mmput(mm);
-out:
-       return result;
-}
-
 /*
  * display mapping lines for a particular process's /proc/pid/maps
  */

diff --git a/include/linux/mm.h b/include/linux/mm.h
index fef602d82722f534aa560884479215df99457630..c31a9cd2a30e03a2672b8fa299c4d6a24a3fa186 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1066,6 +1066,19 @@ extern void unlink_file_vma(struct vm_area_struct *);
 extern struct vm_area_struct *copy_vma(struct vm_area_struct **,
        unsigned long addr, unsigned long len, pgoff_t pgoff);
 extern void exit_mmap(struct mm_struct *);
+
+#ifdef CONFIG_PROC_FS
+/* From fs/proc/base.c. callers must _not_ hold the mm's exe_file_lock */
+extern void added_exe_file_vma(struct mm_struct *mm);
+extern void removed_exe_file_vma(struct mm_struct *mm);
+#else
+static inline void added_exe_file_vma(struct mm_struct *mm)
+{}
+
+static inline void removed_exe_file_vma(struct mm_struct *mm)
+{}
+#endif /* CONFIG_PROC_FS */
+
 extern int may_expand_vm(struct mm_struct *mm, unsigned long npages);
 extern int install_special_mapping(struct mm_struct *mm,
                                   unsigned long addr, unsigned long len,

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index bc97bd54f6060f4ebc023c6ba371498c83a3559c..eb7c16cc95596fae106848e0a66b3b04f6f6b68a 100644 (file)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -229,6 +229,12 @@ struct mm_struct {
        struct task_struct *owner;      /* The thread group leader that */
                                        /* owns the mm_struct.          */
 #endif
+
+#ifdef CONFIG_PROC_FS
+       /* store ref to file /proc/<pid>/exe symlink points to */
+       struct file *exe_file;
+       unsigned long num_exe_file_vmas;
+#endif
 };
 
 #endif /* _LINUX_MM_TYPES_H */

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 9b6c935f69cf6d1986677b968bb17c2ca000e4b0..65f2299b772b7bf004a5ea3456955dd015aff714 100644 (file)
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -9,7 +9,6 @@
 
 struct net;
 struct completion;
-
 /*
  * The proc filesystem constants/structures
  */
@@ -206,6 +205,12 @@ extern void proc_net_remove(struct net *net, const char *name);
 extern struct proc_dir_entry *proc_net_mkdir(struct net *net, const char *name,
        struct proc_dir_entry *parent);
 
+/* While the {get|set|dup}_mm_exe_file functions are for mm_structs, they are
+ * only needed to implement /proc/<pid>|self/exe so we define them here. */
+extern void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file);
+extern struct file *get_mm_exe_file(struct mm_struct *mm);
+extern void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm);
+
 #else
 
 #define proc_root_driver NULL
@@ -255,6 +260,19 @@ static inline void pid_ns_release_proc(struct pid_namespace *ns)
 {
 }
 
+static inline void set_mm_exe_file(struct mm_struct *mm,
+                                  struct file *new_exe_file)
+{}
+
+static inline struct file *get_mm_exe_file(struct mm_struct *mm)
+{
+       return NULL;
+}
+
+static inline void dup_mm_exe_file(struct mm_struct *oldmm,
+                                  struct mm_struct *newmm)
+{}
+
 #endif /* CONFIG_PROC_FS */
 
 #if !defined(CONFIG_PROC_KCORE)

diff --git a/kernel/fork.c b/kernel/fork.c
index de5c16c6b6ecd10b6898f2fc47062c987d851d36..068ffe007529155dfc7b6d199c2afbd9219d8b74 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -431,6 +431,7 @@ void mmput(struct mm_struct *mm)
        if (atomic_dec_and_test(&mm->mm_users)) {
                exit_aio(mm);
                exit_mmap(mm);
+               set_mm_exe_file(mm, NULL);
                if (!list_empty(&mm->mmlist)) {
                        spin_lock(&mmlist_lock);
                        list_del(&mm->mmlist);
@@ -543,6 +544,8 @@ struct mm_struct *dup_mm(struct task_struct *tsk)
        if (init_new_context(tsk, mm))
                goto fail_nocontext;
 
+       dup_mm_exe_file(oldmm, mm);
+
        err = dup_mmap(mm, oldmm);
        if (err)
                goto free_pt;

diff --git a/mm/mmap.c b/mm/mmap.c
index 677d184b0d42d0d9d10311569872589b7a1e2ef4..fac66337da2a3bcd3a003ba9d33096938c17fb57 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -230,8 +230,11 @@ static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
        might_sleep();
        if (vma->vm_ops && vma->vm_ops->close)
                vma->vm_ops->close(vma);
-       if (vma->vm_file)
+       if (vma->vm_file) {
                fput(vma->vm_file);
+               if (vma->vm_flags & VM_EXECUTABLE)
+                       removed_exe_file_vma(vma->vm_mm);
+       }
        mpol_put(vma_policy(vma));
        kmem_cache_free(vm_area_cachep, vma);
        return next;
@@ -623,8 +626,11 @@ again:                     remove_next = 1 + (end > next->vm_end);
                spin_unlock(&mapping->i_mmap_lock);
 
        if (remove_next) {
-               if (file)
+               if (file) {
                        fput(file);
+                       if (next->vm_flags & VM_EXECUTABLE)
+                               removed_exe_file_vma(mm);
+               }
                mm->map_count--;
                mpol_put(vma_policy(next));
                kmem_cache_free(vm_area_cachep, next);
@@ -1154,6 +1160,8 @@ munmap_back:
                error = file->f_op->mmap(file, vma);
                if (error)
                        goto unmap_and_free_vma;
+               if (vm_flags & VM_EXECUTABLE)
+                       added_exe_file_vma(mm);
        } else if (vm_flags & VM_SHARED) {
                error = shmem_zero_setup(vma);
                if (error)
@@ -1185,6 +1193,8 @@ munmap_back:
                mpol_put(vma_policy(vma));
                kmem_cache_free(vm_area_cachep, vma);
                fput(file);
+               if (vm_flags & VM_EXECUTABLE)
+                       removed_exe_file_vma(mm);
        } else {
                vma_link(mm, vma, prev, rb_link, rb_parent);
                file = vma->vm_file;
@@ -1817,8 +1827,11 @@ int split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
        }
        vma_set_policy(new, pol);
 
-       if (new->vm_file)
+       if (new->vm_file) {
                get_file(new->vm_file);
+               if (vma->vm_flags & VM_EXECUTABLE)
+                       added_exe_file_vma(mm);
+       }
 
        if (new->vm_ops && new->vm_ops->open)
                new->vm_ops->open(new);
@@ -2135,8 +2148,11 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
                        new_vma->vm_start = addr;
                        new_vma->vm_end = addr + len;
                        new_vma->vm_pgoff = pgoff;
-                       if (new_vma->vm_file)
+                       if (new_vma->vm_file) {
                                get_file(new_vma->vm_file);
+                               if (vma->vm_flags & VM_EXECUTABLE)
+                                       added_exe_file_vma(mm);
+                       }
                        if (new_vma->vm_ops && new_vma->vm_ops->open)
                                new_vma->vm_ops->open(new_vma);
                        vma_link(mm, new_vma, prev, rb_link, rb_parent);

diff --git a/mm/nommu.c b/mm/nommu.c
index 1d32fe89d57b18642283a419600828584354d469..ef8c62cec697a06495b13f2658aff4e30000065c 100644 (file)
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -966,8 +966,13 @@ unsigned long do_mmap_pgoff(struct file *file,
 
        INIT_LIST_HEAD(&vma->anon_vma_node);
        atomic_set(&vma->vm_usage, 1);
-       if (file)
+       if (file) {
                get_file(file);
+               if (vm_flags & VM_EXECUTABLE) {
+                       added_exe_file_vma(current->mm);
+                       vma->vm_mm = current->mm;
+               }
+       }
        vma->vm_file    = file;
        vma->vm_flags   = vm_flags;
        vma->vm_start   = addr;
@@ -1022,8 +1027,11 @@ unsigned long do_mmap_pgoff(struct file *file,
        up_write(&nommu_vma_sem);
        kfree(vml);
        if (vma) {
-               if (vma->vm_file)
+               if (vma->vm_file) {
                        fput(vma->vm_file);
+                       if (vma->vm_flags & VM_EXECUTABLE)
+                               removed_exe_file_vma(vma->vm_mm);
+               }
                kfree(vma);
        }
        return ret;
@@ -1053,7 +1061,7 @@ EXPORT_SYMBOL(do_mmap_pgoff);
 /*
  * handle mapping disposal for uClinux
  */
-static void put_vma(struct vm_area_struct *vma)
+static void put_vma(struct mm_struct *mm, struct vm_area_struct *vma)
 {
        if (vma) {
                down_write(&nommu_vma_sem);
@@ -1075,8 +1083,11 @@ static void put_vma(struct vm_area_struct *vma)
                        realalloc -= kobjsize(vma);
                        askedalloc -= sizeof(*vma);
 
-                       if (vma->vm_file)
+                       if (vma->vm_file) {
                                fput(vma->vm_file);
+                               if (vma->vm_flags & VM_EXECUTABLE)
+                                       removed_exe_file_vma(mm);
+                       }
                        kfree(vma);
                }
 
@@ -1113,7 +1124,7 @@ int do_munmap(struct mm_struct *mm, unsigned long addr, size_t len)
  found:
        vml = *parent;
 
-       put_vma(vml->vma);
+       put_vma(mm, vml->vma);
 
        *parent = vml->next;
        realalloc -= kobjsize(vml);
@@ -1158,7 +1169,7 @@ void exit_mmap(struct mm_struct * mm)
 
                while ((tmp = mm->context.vmlist)) {
                        mm->context.vmlist = tmp->next;
-                       put_vma(tmp->vma);
+                       put_vma(mm, tmp->vma);
 
                        realalloc -= kobjsize(tmp);
                        askedalloc -= sizeof(*tmp);