[10/23] proc: protect mm start_code/end_code in /proc/pid/stat

[Greg KH]

From: Kees Cook <kees.cook@xxxxxxxxxxxxx>

commit 5883f57ca0008ffc93e09cbb9847a1928e50c6f3 upstream.

While mm->start_stack was protected from cross-uid viewing (commit
f83ce3e6b02d5 ("proc: avoid information leaks to non-privileged
processes")), the start_code and end_code values were not.  This would
allow the text location of a PIE binary to leak, defeating ASLR.

Note that the value "1" is used instead of "0" for a protected value since
"ps", "killall", and likely other readers of /proc/pid/stat, take
start_code of "0" to mean a kernel thread and will misbehave.  Thanks to
Brad Spengler for pointing this out.

Addresses CVE-2011-0726

Signed-off-by: Kees Cook <kees.cook@xxxxxxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Eugene Teo <eugeneteo@xxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Brad Spengler <spender@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 fs/proc/array.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -473,8 +473,8 @@ static int do_task_stat(struct seq_file
 		vsize,
 		mm ? get_mm_rss(mm) : 0,
 		rsslim,
-		mm ? mm->start_code : 0,
-		mm ? mm->end_code : 0,
+		mm ? (permitted ? mm->start_code : 1) : 0,
+		mm ? (permitted ? mm->end_code : 1) : 0,
 		(permitted && mm) ? mm->start_stack : 0,
 		esp,
 		eip,


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