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Subject[PATCH] configfs: fix a race in configfs_lookup()
Date
When configfs_lookup() is executing list_for_each_entry(),
it is possible that configfs_dir_lseek() is calling list_del().
Some unfortunate interleavings of them can cause a kernel NULL
pointer dereference error

Thread 1 Thread 2
//configfs_dir_lseek() //configfs_lookup()
list_del(&cursor->s_sibling);
list_for_each_entry(sd, ...)

Fix this bug by using list_for_each_entry_safe() instead.

Reported-by: Sishuai Gong <sishuai@purdue.edu>
Signed-off-by: sishuaigong <sishuai@purdue.edu>
---
fs/configfs/dir.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index ac5e0c0e9181..8f5d0309fb4a 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -452,7 +452,7 @@ static struct dentry * configfs_lookup(struct inode *dir,
unsigned int flags)
{
struct configfs_dirent * parent_sd = dentry->d_parent->d_fsdata;
- struct configfs_dirent * sd;
+ struct configfs_dirent *sd, *tmp;
int found = 0;
int err;

@@ -468,7 +468,7 @@ static struct dentry * configfs_lookup(struct inode *dir,
if (!configfs_dirent_is_ready(parent_sd))
goto out;

- list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
+ list_for_each_entry_safe(sd, tmp, &parent_sd->s_children, s_sibling) {
if (sd->s_type & CONFIGFS_NOT_PINNED) {
const unsigned char * name = configfs_get_name(sd);

--
2.17.1
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