[PATCH] _proc_do_string(): fix short reads

If you try to read things like /proc/sys/kernel/osrelease with single-byte
reads, you get just one byte and then EOF.  This is because _proc_do_string()
assumes that the caller is read()ing into a buffer which is large enough to
fit the whole string in a single hit.

Fix.

Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 84cab0ce44d9af826ebbbfef5204f9833789b9d4..e0ac6cd79fcf6955c6105815b4c8ab4d9d53e97f 100644 (file)
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1686,13 +1686,12 @@ static int _proc_do_string(void* data, int maxlen, int write,
        size_t len;
        char __user *p;
        char c;
-       
-       if (!data || !maxlen || !*lenp ||
-           (*ppos && !write)) {
+
+       if (!data || !maxlen || !*lenp) {
                *lenp = 0;
                return 0;
        }
-       
+
        if (write) {
                len = 0;
                p = buffer;
@@ -1713,6 +1712,15 @@ static int _proc_do_string(void* data, int maxlen, int write,
                len = strlen(data);
                if (len > maxlen)
                        len = maxlen;
+
+               if (*ppos > len) {
+                       *lenp = 0;
+                       return 0;
+               }
+
+               data += *ppos;
+               len  -= *ppos;
+
                if (len > *lenp)
                        len = *lenp;
                if (len)