In kernel/trace/trace_functions_graph.c, print_graph_duration(), len can
be as low as 1 or 2, which could make snprintf() write beyond the
buffer bounds. (Found by cppcheck, no real-world bug occured)
Signed-off-by: Daniel Mack <[email protected]>
---
kernel/trace/trace_functions_graph.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 930c08e..7533b25 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -281,7 +281,7 @@ print_graph_duration(unsigned long long duration, struct trace_seq *s)
unsigned long nsecs_rem = do_div(duration, 1000);
/* log10(ULONG_MAX) + '\0' */
char msecs_str[21];
- char nsecs_str[5];
+ char nsecs_str[8];
int ret, len;
int i;
--
1.6.2
On Mon, Mar 23, 2009 at 05:10:37PM +0100, Daniel Mack wrote:
> In kernel/trace/trace_functions_graph.c, print_graph_duration(), len can
> be as low as 1 or 2, which could make snprintf() write beyond the
> buffer bounds. (Found by cppcheck, no real-world bug occured)
>
> Signed-off-by: Daniel Mack <[email protected]>
Hi Daniel,
It can't really happen because nsecs_rem is a rest of a division
per 1000, so it will not exceed 3 digits (so it should be [4] and not
[5], btw).
I must confess I should have added a better comment on this
area.
We are printing a duration in usec with a part in nsec with the following
constraints:
_ never exceed 7 characters unless we are are upper 9999999 usecs
_ always keep the usecs consistants
Which means that while we have 4 or lesser digits for the usecs, we can
print the 3 digits of the nanosecs.
If we need 5 for usecs, drop the least significant nanosec digit.
If we need 6 for usecs, drop the two least significant nanosec digits
6754.543 is correct
67545.543 must become 67545.54
etc...
That's why we have:
len = strlen(msecs_str);
/* Print nsecs (we don't want to exceed 7 numbers) */
if (len < 7) {
snprintf(nsecs_str, 8 - len, "%03lu", nsecs_rem);
The 8 - len inside snprintf is not a security against overflow but a
precision set. We know that it will never go upper 3 digits, but if we
have 6 digits for usecs, we want only 8 - 6 = 2 nsecs
Hmm, may be it should be 7 -len. I don't remember. Anyway, this part
must be fixed to handle msecs and align the row to the left...
Frederic.
> ---
> kernel/trace/trace_functions_graph.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 930c08e..7533b25 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -281,7 +281,7 @@ print_graph_duration(unsigned long long duration, struct trace_seq *s)
> unsigned long nsecs_rem = do_div(duration, 1000);
> /* log10(ULONG_MAX) + '\0' */
> char msecs_str[21];
> - char nsecs_str[5];
> + char nsecs_str[8];
> int ret, len;
> int i;
>
> --
> 1.6.2
>
> --
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Commit-ID: 603b9b9081ae0a1af986b9059a0a5055876ddea9
Gitweb: http://git.kernel.org/tip/603b9b9081ae0a1af986b9059a0a5055876ddea9
Author: Daniel Mack <[email protected]>
AuthorDate: Mon, 23 Mar 2009 17:10:37 +0100
Committer: Ingo Molnar <[email protected]>
CommitDate: Mon, 23 Mar 2009 17:40:51 +0100
kernel/trace/trace_functions_graph.c: fix nsecs_str buffer size
Impact: fix currently inactive buffer-overflow
In kernel/trace/trace_functions_graph.c, print_graph_duration(),
len can be as low as 1 or 2, which could make snprintf() write
beyond the buffer bounds. (Found by cppcheck, no real-world bug
occured)
Signed-off-by: Daniel Mack <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
---
kernel/trace/trace_functions_graph.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index e876816..a305472 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -430,7 +430,7 @@ print_graph_duration(unsigned long long duration, struct trace_seq *s)
unsigned long nsecs_rem = do_div(duration, 1000);
/* log10(ULONG_MAX) + '\0' */
char msecs_str[21];
- char nsecs_str[5];
+ char nsecs_str[8];
int ret, len;
int i;
On Mon, Mar 23, 2009 at 04:42:27PM +0000, Daniel Mack wrote:
> Commit-ID: 603b9b9081ae0a1af986b9059a0a5055876ddea9
> Gitweb: http://git.kernel.org/tip/603b9b9081ae0a1af986b9059a0a5055876ddea9
> Author: Daniel Mack <[email protected]>
> AuthorDate: Mon, 23 Mar 2009 17:10:37 +0100
> Committer: Ingo Molnar <[email protected]>
> CommitDate: Mon, 23 Mar 2009 17:40:51 +0100
>
> kernel/trace/trace_functions_graph.c: fix nsecs_str buffer size
>
> Impact: fix currently inactive buffer-overflow
>
> In kernel/trace/trace_functions_graph.c, print_graph_duration(),
> len can be as low as 1 or 2, which could make snprintf() write
> beyond the buffer bounds. (Found by cppcheck, no real-world bug
> occured)
>
> Signed-off-by: Daniel Mack <[email protected]>
> Cc: Steven Rostedt <[email protected]>
> Cc: Frederic Weisbecker <[email protected]>
> LKML-Reference: <[email protected]>
> Signed-off-by: Ingo Molnar <[email protected]>
>
>
> ---
> kernel/trace/trace_functions_graph.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
Ingo, as I explained to Daniel before (I should have Cc you),
there is no overflow to protect here, so this patch will not
change anything.
This is my bad, I should better comment my code.
Frederic.
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index e876816..a305472 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -430,7 +430,7 @@ print_graph_duration(unsigned long long duration, struct trace_seq *s)
> unsigned long nsecs_rem = do_div(duration, 1000);
> /* log10(ULONG_MAX) + '\0' */
> char msecs_str[21];
> - char nsecs_str[5];
> + char nsecs_str[8];
> int ret, len;
> int i;
>
Hi Frederic,
On Mon, Mar 23, 2009 at 05:40:31PM +0100, Frederic Weisbecker wrote:
> It can't really happen because nsecs_rem is a rest of a division
> per 1000, so it will not exceed 3 digits (so it should be [4] and not
> [5], btw).
>
> I must confess I should have added a better comment on this
> area.
>
> We are printing a duration in usec with a part in nsec with the following
> constraints:
>
> _ never exceed 7 characters unless we are are upper 9999999 usecs
> _ always keep the usecs consistants
>
> Which means that while we have 4 or lesser digits for the usecs, we can
> print the 3 digits of the nanosecs.
>
> If we need 5 for usecs, drop the least significant nanosec digit.
> If we need 6 for usecs, drop the two least significant nanosec digits
Ok, I see. I was just confused about the max len argument to snprintf()
(and so was cppcheck), but at a closer look, this can't become a
problem.
Nevermind, drop the patch - but good that we talked about it :)
Daniel
* Frederic Weisbecker <[email protected]> wrote:
> On Mon, Mar 23, 2009 at 04:42:27PM +0000, Daniel Mack wrote:
> > Commit-ID: 603b9b9081ae0a1af986b9059a0a5055876ddea9
> > Gitweb: http://git.kernel.org/tip/603b9b9081ae0a1af986b9059a0a5055876ddea9
> > Author: Daniel Mack <[email protected]>
> > AuthorDate: Mon, 23 Mar 2009 17:10:37 +0100
> > Committer: Ingo Molnar <[email protected]>
> > CommitDate: Mon, 23 Mar 2009 17:40:51 +0100
> >
> > kernel/trace/trace_functions_graph.c: fix nsecs_str buffer size
> >
> > Impact: fix currently inactive buffer-overflow
> >
> > In kernel/trace/trace_functions_graph.c, print_graph_duration(),
> > len can be as low as 1 or 2, which could make snprintf() write
> > beyond the buffer bounds. (Found by cppcheck, no real-world bug
> > occured)
> >
> > Signed-off-by: Daniel Mack <[email protected]>
> > Cc: Steven Rostedt <[email protected]>
> > Cc: Frederic Weisbecker <[email protected]>
> > LKML-Reference: <[email protected]>
> > Signed-off-by: Ingo Molnar <[email protected]>
> >
> >
> > ---
> > kernel/trace/trace_functions_graph.c | 2 +-
> > 1 files changed, 1 insertions(+), 1 deletions(-)
>
>
>
> Ingo, as I explained to Daniel before (I should have Cc you),
> there is no overflow to protect here, so this patch will not
> change anything.
>
> This is my bad, I should better comment my code.
Yeah - saw your reply, and zapped the commit already. Please add a
comment in any case.
Ingo