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| author | Sahitya Tummala <stummala@codeaurora.org> | 2019-01-03 12:18:15 +0100 |
|---|---|---|
| committer | Christoph Hellwig <hch@lst.de> | 2019-05-28 08:11:58 +0200 |
| commit | f6122ed2a4f9c9c1c073ddf6308d1b2ac10e0781 (patch) | |
| tree | f0740d5387ddff7ad1251dcfb101864a729dce75 /fs/configfs | |
| parent | Linux 5.2-rc2 (diff) | |
| download | linux-f6122ed2a4f9c9c1c073ddf6308d1b2ac10e0781.tar.xz linux-f6122ed2a4f9c9c1c073ddf6308d1b2ac10e0781.zip | |
configfs: Fix use-after-free when accessing sd->s_dentry
In the vfs_statx() context, during path lookup, the dentry gets
added to sd->s_dentry via configfs_attach_attr(). In the end,
vfs_statx() kills the dentry by calling path_put(), which invokes
configfs_d_iput(). Ideally, this dentry must be removed from
sd->s_dentry but it doesn't if the sd->s_count >= 3. As a result,
sd->s_dentry is holding reference to a stale dentry pointer whose
memory is already freed up. This results in use-after-free issue,
when this stale sd->s_dentry is accessed later in
configfs_readdir() path.
This issue can be easily reproduced, by running the LTP test case -
sh fs_racer_file_list.sh /config
(https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/fs/racer/fs_racer_file_list.sh)
Fixes: 76ae281f6307 ('configfs: fix race between dentry put and lookup')
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Diffstat (limited to 'fs/configfs')
| -rw-r--r-- | fs/configfs/dir.c | 14 |
1 files changed, 6 insertions, 8 deletions
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c index 5e7932d668ab..22203a3423a3 100644 --- a/fs/configfs/dir.c +++ b/fs/configfs/dir.c @@ -58,15 +58,13 @@ static void configfs_d_iput(struct dentry * dentry, if (sd) { /* Coordinate with configfs_readdir */ spin_lock(&configfs_dirent_lock); - /* Coordinate with configfs_attach_attr where will increase - * sd->s_count and update sd->s_dentry to new allocated one. - * Only set sd->dentry to null when this dentry is the only - * sd owner. - * If not do so, configfs_d_iput may run just after - * configfs_attach_attr and set sd->s_dentry to null - * even it's still in use. + /* + * Set sd->s_dentry to null only when this dentry is the one + * that is going to be killed. Otherwise configfs_d_iput may + * run just after configfs_attach_attr and set sd->s_dentry to + * NULL even it's still in use. */ - if (atomic_read(&sd->s_count) <= 2) + if (sd->s_dentry == dentry) sd->s_dentry = NULL; spin_unlock(&configfs_dirent_lock); |