* Re: [PATCH v2] blktrace: fix dereference after null check
2020-03-04 10:58 [PATCH v2] blktrace: fix dereference after null check Cengiz Can
@ 2020-03-05 8:47 ` Ming Lei
2020-03-05 10:13 ` Bob Liu
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Ming Lei @ 2020-03-05 8:47 UTC (permalink / raw)
To: Cengiz Can
Cc: Jens Axboe, Steven Rostedt, Ingo Molnar, linux-block,
Linux Kernel Mailing List
On Wed, Mar 4, 2020 at 6:59 PM Cengiz Can <cengiz@kernel.wtf> wrote:
>
> There was a recent change in blktrace.c that added a RCU protection to
> `q->blk_trace` in order to fix a use-after-free issue during access.
>
> However the change missed an edge case that can lead to dereferencing of
> `bt` pointer even when it's NULL:
>
> Coverity static analyzer marked this as a FORWARD_NULL issue with CID
> 1460458.
>
> ```
> /kernel/trace/blktrace.c: 1904 in sysfs_blk_trace_attr_store()
> 1898 ret = 0;
> 1899 if (bt == NULL)
> 1900 ret = blk_trace_setup_queue(q, bdev);
> 1901
> 1902 if (ret == 0) {
> 1903 if (attr == &dev_attr_act_mask)
> >>> CID 1460458: Null pointer dereferences (FORWARD_NULL)
> >>> Dereferencing null pointer "bt".
> 1904 bt->act_mask = value;
> 1905 else if (attr == &dev_attr_pid)
> 1906 bt->pid = value;
> 1907 else if (attr == &dev_attr_start_lba)
> 1908 bt->start_lba = value;
> 1909 else if (attr == &dev_attr_end_lba)
> ```
>
> Added a reassignment with RCU annotation to fix the issue.
>
> Fixes: c780e86dd48 ("blktrace: Protect q->blk_trace with RCU")
>
> Signed-off-by: Cengiz Can <cengiz@kernel.wtf>
> ---
>
> Patch Changelog
> * v2: Added RCU annotation to assignment
>
> kernel/trace/blktrace.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index 4560878f0bac..ca39dc3230cb 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -1896,8 +1896,11 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
> }
>
> ret = 0;
> - if (bt == NULL)
> + if (bt == NULL) {
> ret = blk_trace_setup_queue(q, bdev);
> + bt = rcu_dereference_protected(q->blk_trace,
> + lockdep_is_held(&q->blk_trace_mutex));
> + }
>
> if (ret == 0) {
> if (attr == &dev_attr_act_mask)
> --
> 2.25.1
>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
--
Ming Lei
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH v2] blktrace: fix dereference after null check
2020-03-04 10:58 [PATCH v2] blktrace: fix dereference after null check Cengiz Can
2020-03-05 8:47 ` Ming Lei
@ 2020-03-05 10:13 ` Bob Liu
2020-03-05 14:05 ` Steven Rostedt
2020-03-05 20:43 ` Jens Axboe
3 siblings, 0 replies; 5+ messages in thread
From: Bob Liu @ 2020-03-05 10:13 UTC (permalink / raw)
To: Cengiz Can, Jens Axboe, Steven Rostedt, Ingo Molnar
Cc: linux-block, linux-kernel
On 3/4/20 6:58 PM, Cengiz Can wrote:
> There was a recent change in blktrace.c that added a RCU protection to
> `q->blk_trace` in order to fix a use-after-free issue during access.
>
> However the change missed an edge case that can lead to dereferencing of
> `bt` pointer even when it's NULL:
>
> Coverity static analyzer marked this as a FORWARD_NULL issue with CID
> 1460458.
>
> ```
> /kernel/trace/blktrace.c: 1904 in sysfs_blk_trace_attr_store()
> 1898 ret = 0;
> 1899 if (bt == NULL)
> 1900 ret = blk_trace_setup_queue(q, bdev);
> 1901
> 1902 if (ret == 0) {
> 1903 if (attr == &dev_attr_act_mask)
>>>> CID 1460458: Null pointer dereferences (FORWARD_NULL)
>>>> Dereferencing null pointer "bt".
> 1904 bt->act_mask = value;
> 1905 else if (attr == &dev_attr_pid)
> 1906 bt->pid = value;
> 1907 else if (attr == &dev_attr_start_lba)
> 1908 bt->start_lba = value;
> 1909 else if (attr == &dev_attr_end_lba)
> ```
>
> Added a reassignment with RCU annotation to fix the issue.
>
> Fixes: c780e86dd48 ("blktrace: Protect q->blk_trace with RCU")
>
> Signed-off-by: Cengiz Can <cengiz@kernel.wtf>
This version looks good to me, thanks.
Reviewed-by: Bob Liu <bob.liu@oracle.com>
> ---
>
> Patch Changelog
> * v2: Added RCU annotation to assignment
>
> kernel/trace/blktrace.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index 4560878f0bac..ca39dc3230cb 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -1896,8 +1896,11 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
> }
>
> ret = 0;
> - if (bt == NULL)
> + if (bt == NULL) {
> ret = blk_trace_setup_queue(q, bdev);
> + bt = rcu_dereference_protected(q->blk_trace,
> + lockdep_is_held(&q->blk_trace_mutex));
> + }
>
> if (ret == 0) {
> if (attr == &dev_attr_act_mask)
> --
> 2.25.1
>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH v2] blktrace: fix dereference after null check
2020-03-04 10:58 [PATCH v2] blktrace: fix dereference after null check Cengiz Can
2020-03-05 8:47 ` Ming Lei
2020-03-05 10:13 ` Bob Liu
@ 2020-03-05 14:05 ` Steven Rostedt
2020-03-05 20:43 ` Jens Axboe
3 siblings, 0 replies; 5+ messages in thread
From: Steven Rostedt @ 2020-03-05 14:05 UTC (permalink / raw)
To: Cengiz Can; +Cc: Jens Axboe, Ingo Molnar, linux-block, linux-kernel
On Wed, 4 Mar 2020 13:58:19 +0300
Cengiz Can <cengiz@kernel.wtf> wrote:
> There was a recent change in blktrace.c that added a RCU protection to
> `q->blk_trace` in order to fix a use-after-free issue during access.
>
> However the change missed an edge case that can lead to dereferencing of
> `bt` pointer even when it's NULL:
>
> Coverity static analyzer marked this as a FORWARD_NULL issue with CID
> 1460458.
>
> ```
> /kernel/trace/blktrace.c: 1904 in sysfs_blk_trace_attr_store()
> 1898 ret = 0;
> 1899 if (bt == NULL)
> 1900 ret = blk_trace_setup_queue(q, bdev);
> 1901
> 1902 if (ret == 0) {
> 1903 if (attr == &dev_attr_act_mask)
> >>> CID 1460458: Null pointer dereferences (FORWARD_NULL)
> >>> Dereferencing null pointer "bt".
> 1904 bt->act_mask = value;
> 1905 else if (attr == &dev_attr_pid)
> 1906 bt->pid = value;
> 1907 else if (attr == &dev_attr_start_lba)
> 1908 bt->start_lba = value;
> 1909 else if (attr == &dev_attr_end_lba)
> ```
>
> Added a reassignment with RCU annotation to fix the issue.
>
> Fixes: c780e86dd48 ("blktrace: Protect q->blk_trace with RCU")
>
> Signed-off-by: Cengiz Can <cengiz@kernel.wtf>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-- Steve
> ---
>
> Patch Changelog
> * v2: Added RCU annotation to assignment
>
> kernel/trace/blktrace.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index 4560878f0bac..ca39dc3230cb 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -1896,8 +1896,11 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
> }
>
> ret = 0;
> - if (bt == NULL)
> + if (bt == NULL) {
> ret = blk_trace_setup_queue(q, bdev);
> + bt = rcu_dereference_protected(q->blk_trace,
> + lockdep_is_held(&q->blk_trace_mutex));
> + }
>
> if (ret == 0) {
> if (attr == &dev_attr_act_mask)
> --
> 2.25.1
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH v2] blktrace: fix dereference after null check
2020-03-04 10:58 [PATCH v2] blktrace: fix dereference after null check Cengiz Can
` (2 preceding siblings ...)
2020-03-05 14:05 ` Steven Rostedt
@ 2020-03-05 20:43 ` Jens Axboe
3 siblings, 0 replies; 5+ messages in thread
From: Jens Axboe @ 2020-03-05 20:43 UTC (permalink / raw)
To: Cengiz Can, Steven Rostedt, Ingo Molnar; +Cc: linux-block, linux-kernel
On 3/4/20 3:58 AM, Cengiz Can wrote:
> There was a recent change in blktrace.c that added a RCU protection to
> `q->blk_trace` in order to fix a use-after-free issue during access.
>
> However the change missed an edge case that can lead to dereferencing of
> `bt` pointer even when it's NULL:
>
> Coverity static analyzer marked this as a FORWARD_NULL issue with CID
> 1460458.
>
> ```
> /kernel/trace/blktrace.c: 1904 in sysfs_blk_trace_attr_store()
> 1898 ret = 0;
> 1899 if (bt == NULL)
> 1900 ret = blk_trace_setup_queue(q, bdev);
> 1901
> 1902 if (ret == 0) {
> 1903 if (attr == &dev_attr_act_mask)
>>>> CID 1460458: Null pointer dereferences (FORWARD_NULL)
>>>> Dereferencing null pointer "bt".
> 1904 bt->act_mask = value;
> 1905 else if (attr == &dev_attr_pid)
> 1906 bt->pid = value;
> 1907 else if (attr == &dev_attr_start_lba)
> 1908 bt->start_lba = value;
> 1909 else if (attr == &dev_attr_end_lba)
> ```
>
> Added a reassignment with RCU annotation to fix the issue.
Applied, thanks.
--
Jens Axboe
^ permalink raw reply [flat|nested] 5+ messages in thread