diff options
author | Eric Biggers <ebiggers@google.com> | 2020-01-24 07:12:34 +0300 |
---|---|---|
committer | Theodore Ts'o <tytso@mit.edu> | 2020-01-25 06:35:03 +0300 |
commit | ec772f01307a2c06ebf6cdd221e6b518a71ddae7 (patch) | |
tree | 9bfe61fd04467699009cc4094ee7d473c3e2dcfb | |
parent | 244adf6426ee31a83f397b700d964cff12a247d3 (diff) | |
download | linux-ec772f01307a2c06ebf6cdd221e6b518a71ddae7.tar.xz |
ext4: fix race conditions in ->d_compare() and ->d_hash()
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>
-rw-r--r-- | fs/ext4/dir.c | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c index 8964778aabef..0129d1462988 100644 --- a/fs/ext4/dir.c +++ b/fs/ext4/dir.c @@ -671,9 +671,11 @@ static int ext4_d_compare(const struct dentry *dentry, unsigned int len, 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); @@ -686,10 +688,11 @@ static int ext4_d_hash(const struct dentry *dentry, struct qstr *str) { 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); |