Prev: i915 drm BUG: unable to handle kernel paging request at a5e89046
Next: [PATCH] acpi: fix apei related table size checking
From: Joe Perches on 23 Jul 2010 13:50
On Fri, 2010-07-23 at 12:04 +0200, Dan Carpenter wrote:
> This is a smatch thing. I suppose someday I will fix smatch to
> evaulate the strings themselves and verify that the buffer is large
> enough. But for now it's nice to be able to automatically check that
> the buffers don't overflow.

There are also many repeated uses of snprintf in kernel sources
that could similarly be a problem.

bar += snprintf(foo + bar, ...)
bar += snprintf(foo + bar, ...)
or
foo += snprintf(foo, ...)
foo += snprintf(foo, ...)

For instance:

$ grep -P -n -A 4 -m 3 "\+=\s*snprintf" drivers/net/wireless/ath/ath5k/debug.c
210: len += snprintf(buf+len, sizeof(buf)-len,
211- "%-24s0x%08x\tintval: %d\tTIM: 0x%x\n",
212- "AR5K_BEACON", v, v & AR5K_BEACON_PERIOD,
213- (v & AR5K_BEACON_TIM) >> AR5K_BEACON_TIM_S);
214-
215: len += snprintf(buf+len, sizeof(buf)-len, "%-24s0x%08x\n",
216- "AR5K_LAST_TSTP", ath5k_hw_reg_read(sc->ah, AR5K_LAST_TSTP));
217-
218: len += snprintf(buf+len, sizeof(buf)-len, "%-24s0x%08x\n\n",
219- "AR5K_BEACON_CNT", ath5k_hw_reg_read(sc->ah, AR5K_BEACON_CNT));
220-

A conversion from snprintf to scnprintf might be appropriate
for those patterns.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
From: Linus Torvalds on 23 Jul 2010 15:30
On Fri, Jul 23, 2010 at 10:48 AM, Joe Perches <joe(a)perches.com> wrote:
>
> There are also many repeated uses of snprintf in kernel sources
> that could similarly be a problem.
>
> � � � �bar += snprintf(foo + bar, ...)
> � � � �bar += snprintf(foo + bar, ...)
> or
> � � � �foo += snprintf(foo, ...)
> � � � �foo += snprintf(foo, ...)

As long as the number of bytes is updated correctly, this won't be a
security problem, although it can cause a (single) warning. The kernel
vsnprintf does

if (WARN_ON_ONCE((int) size < 0))
return 0;

so if somebody overflows a buffer with multiple snprintf calls, it
will all be ok as long as the buffer size thing is updated the natural
way (possibly using pointer arithmetic, eg "end - bar").

Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
 | 
Pages: 1
Prev: i915 drm BUG: unable to handle kernel paging request at a5e89046
Next: [PATCH] acpi: fix apei related table size checking