[PATCH] char: istallion: fix arbitrary kernel memory reads/writes

From: Vasiliy Kulikov
Date: Sat Apr 09 2011 - 08:41:37 EST

stli_brdstats is defined as global variable. After de-BKL-ization in
the patch b4eda9cb48eac1b7 an access to the variable is not serialized
anymore. This leads to the TOCTOU in stli_getbrdstats():

if (copy_from_user(&stli_brdstats, bp, sizeof(combrd_t)))
return -EFAULT;
if (stli_brdstats.brd >= STL_MAXBRDS) <<<<
return -ENODEV;
brdp = stli_brds[stli_brdstats.brd]; <<<<

If one process calls COM_GETBRDSTATS ioctl() with sane .brd, second
process calls COM_GETBRDSTATS ioctl() with invalid .brd, and the
second process' copy_from_user() executes exactly between the check and
stli_brds[] indexation of the first process, then the first process gets
contents of memory at *stli_brds[stli_brdstats.brd] address. Also
the resulting .nrpanels field may be too big, in this case
stli_brdstats.panels array overflows.

Signed-off-by: Vasiliy Kulikov <segoon@xxxxxxxxxxxx>
drivers/char/istallion.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/char/istallion.c b/drivers/char/istallion.c
index 7c6de4c..232c5e0 100644
--- a/drivers/char/istallion.c
+++ b/drivers/char/istallion.c
@@ -186,7 +186,6 @@ static struct ktermios stli_deftermios = {
* re-used for each stats call.
static comstats_t stli_comstats;
-static combrd_t stli_brdstats;
static struct asystats stli_cdkstats;

@@ -4005,6 +4004,7 @@ static int stli_getbrdstats(combrd_t __user *bp)
struct stlibrd *brdp;
unsigned int i;
+ combrd_t stli_brdstats;

if (copy_from_user(&stli_brdstats, bp, sizeof(combrd_t)))
return -EFAULT;

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