[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>

1 files changed, 12 insertions, 4 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 84cab0ce44d9..e0ac6cd79fcf 100644
--- 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)