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configfs: fix a race in configfs_lookup()

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commit c42dd069be upstream.

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 by grabbing configfs_dirent_lock in configfs_lookup()
while iterating ->s_children.

Signed-off-by: Sishuai Gong <sishuai@purdue.edu>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kyle Zeng <zengyhkyle@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Sishuai Gong 2021-08-25 07:52:20 +02:00 committed by Greg Kroah-Hartman
parent 746b363bef
commit c709c7ca02
1 changed files with 2 additions and 0 deletions
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2
fs/configfs/dir.c
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@ -479,6 +479,7 @@ static struct dentry * configfs_lookup(struct inode *dir,
if (!configfs_dirent_is_ready(parent_sd))
goto out;
spin_lock(&configfs_dirent_lock);
list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
if (sd->s_type & CONFIGFS_NOT_PINNED) {
const unsigned char * name = configfs_get_name(sd);
@ -491,6 +492,7 @@ static struct dentry * configfs_lookup(struct inode *dir,
break;
}
}
spin_unlock(&configfs_dirent_lock);
if (!found) {
/*