/proc/sysvipc/shm: fix 32-bit truncation of segment sizes

sysvipc_shm_proc_show() picks between format strings (based on the
expected maximum length of a SHM segment) in a way that prevents gcc from
performing format checks on the seq_printf() parameters.  This hid two
format errors - shp->shm_segsz and shp->shm_nattach are both unsigned
long, but were being printed as unsigned int and signed int respectively.
This leads to 32-bit truncation of SHM segment sizes reported in
/proc/sysvipc/shm.  (And for nattach, but that's less of a problem for
most users).

This patch makes the format string directly visible to gcc's format
specifier checker, and fixes the two broken format specifiers.

Signed-off-by: Paul Menage <menage@google.com>
Cc: Nadia Derbey <Nadia.Derbey@bull.net>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Pierre Peiffer <peifferp@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 8 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index d05f6b564998..790240cd067f 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1058,16 +1058,16 @@ asmlinkage long sys_shmdt(char __user *shmaddr)
 static int sysvipc_shm_proc_show(struct seq_file *s, void *it)
 {
         struct shmid_kernel *shp = it;
-        char *format;
 
-#define SMALL_STRING "%10d %10d  %4o %10u %5u %5u  %5d %5u %5u %5u %5u %10lu %10lu %10lu\n"
-#define BIG_STRING   "%10d %10d  %4o %21u %5u %5u  %5d %5u %5u %5u %5u %10lu %10lu %10lu\n"
+#if BITS_PER_LONG <= 32
+#define SIZE_SPEC "%10lu"
+#else
+#define SIZE_SPEC "%21lu"
+#endif
 
-        if (sizeof(size_t) <= sizeof(int))
-                format = SMALL_STRING;
-        else
-                format = BIG_STRING;
-        return seq_printf(s, format,
+        return seq_printf(s,
+                          "%10d %10d  %4o " SIZE_SPEC " %5u %5u  "
+                          "%5lu %5u %5u %5u %5u %10lu %10lu %10lu\n",
                           shp->shm_perm.key,
                           shp->shm_perm.id,
                           shp->shm_perm.mode,