blktrace: fix dereference after null check

This commit is contained in:
Salvatore Bonaccorso 2020-04-26 11:27:18 +02:00
parent a5acdf855d
commit 65ba05e78d
3 changed files with 68 additions and 0 deletions

1
debian/changelog vendored
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@ -1818,6 +1818,7 @@ linux (4.19.118-1) UNRELEASED; urgency=medium
* net: ipv6_stub: use ip6_dst_lookup_flow instead of ip6_dst_lookup
(CVE-2020-1749)
* blktrace: Protect q->blk_trace with RCU (CVE-2019-19768)
* blktrace: fix dereference after null check
[ Ben Hutchings ]
* [x86] Drop "Add a SysRq option to lift kernel lockdown" (Closes: #947021)

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@ -0,0 +1,66 @@
From: Cengiz Can <cengiz@kernel.wtf>
Date: Wed, 4 Mar 2020 13:58:19 +0300
Subject: blktrace: fix dereference after null check
Origin: https://git.kernel.org/linus/153031a301bb07194e9c37466cfce8eacb977621
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")
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bob Liu <bob.liu@oracle.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Cengiz Can <cengiz@kernel.wtf>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 99f6cdbf2f540..6cea8bbca03cb 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -1893,8 +1893,11 @@ 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)
--
2.20.1

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@ -298,5 +298,6 @@ bugfix/all/f2fs-fix-to-avoid-memory-leakage-in-f2fs_listxattr.patch
bugfix/all/net-ipv6-add-net-argument-to-ip6_dst_lookup_flow.patch
bugfix/all/net-ipv6_stub-use-ip6_dst_lookup_flow-instead-of-ip6.patch
bugfix/all/blktrace-protect-q-blk_trace-with-rcu.patch
bugfix/all/blktrace-fix-dereference-after-null-check.patch
# ABI maintenance