From: Eric Biggers ebiggers@google.com
commit ec772f01307a2c06ebf6cdd221e6b518a71ddae7 upstream.
Since ->d_compare() and ->d_hash() can be called in RCU-walk mode, ->d_parent and ->d_inode can be concurrently modified, and in particular, ->d_inode may be changed to NULL. For ext4_d_hash() this resulted in a reproducible NULL dereference if a lookup is done in a directory being deleted, e.g. with:
int main() { if (fork()) { for (;;) { mkdir("subdir", 0700); rmdir("subdir"); } } else { for (;;) access("subdir/file", 0); } }
... or by running the 't_encrypted_d_revalidate' program from xfstests. Both repros work in any directory on a filesystem with the encoding feature, even if the directory doesn't actually have the casefold flag.
I couldn't reproduce a crash in ext4_d_compare(), but it appears that a similar crash is possible there.
Fix these bugs by reading ->d_parent and ->d_inode using READ_ONCE() and falling back to the case sensitive behavior if the inode is NULL.
Reported-by: Al Viro viro@zeniv.linux.org.uk Fixes: b886ee3e778e ("ext4: Support case-insensitive file name lookups") Cc: stable@vger.kernel.org # v5.2+ Signed-off-by: Eric Biggers ebiggers@google.com Link: https://lore.kernel.org/r/20200124041234.159740-1-ebiggers@kernel.org Signed-off-by: Theodore Ts'o tytso@mit.edu Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/ext4/dir.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
--- a/fs/ext4/dir.c +++ b/fs/ext4/dir.c @@ -672,9 +672,11 @@ static int ext4_d_compare(const struct d const char *str, const struct qstr *name) { struct qstr qstr = {.name = str, .len = len }; - struct inode *inode = dentry->d_parent->d_inode; + const struct dentry *parent = READ_ONCE(dentry->d_parent); + const struct inode *inode = READ_ONCE(parent->d_inode);
- if (!IS_CASEFOLDED(inode) || !EXT4_SB(inode->i_sb)->s_encoding) { + if (!inode || !IS_CASEFOLDED(inode) || + !EXT4_SB(inode->i_sb)->s_encoding) { if (len != name->len) return -1; return memcmp(str, name->name, len); @@ -687,10 +689,11 @@ static int ext4_d_hash(const struct dent { const struct ext4_sb_info *sbi = EXT4_SB(dentry->d_sb); const struct unicode_map *um = sbi->s_encoding; + const struct inode *inode = READ_ONCE(dentry->d_inode); unsigned char *norm; int len, ret = 0;
- if (!IS_CASEFOLDED(dentry->d_inode) || !um) + if (!inode || !IS_CASEFOLDED(inode) || !um) return 0;
norm = kmalloc(PATH_MAX, GFP_ATOMIC);