| Message ID | 20200304105818.11781-1-cengiz@kernel.wtf (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
| Series | [v2] blktrace: fix dereference after null check | expand |
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>
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 >
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
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.
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)
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(-) -- 2.25.1