This is a note to let you know that I've just added the patch titled f2fs: fix race conditions in ->d_compare() and ->d_hash() to the 5.5-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: f2fs-fix-race-conditions-in-d_compare-and-d_hash.patch and it can be found in the queue-5.5 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 80f2388afa6ef985f9c5c228e36705c4d4db4756 Mon Sep 17 00:00:00 2001 From: Eric Biggers <ebiggers@xxxxxxxxxx> Date: Thu, 23 Jan 2020 20:15:49 -0800 Subject: f2fs: fix race conditions in ->d_compare() and ->d_hash() From: Eric Biggers <ebiggers@xxxxxxxxxx> commit 80f2388afa6ef985f9c5c228e36705c4d4db4756 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 f2fs_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 f2fs_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@xxxxxxxxxxxxxxxxxx> Fixes: 2c2eb7a300cd ("f2fs: Support case-insensitive file name lookups") Cc: <stable@xxxxxxxxxxxxxxx> # v5.4+ Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/f2fs/dir.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) --- a/fs/f2fs/dir.c +++ b/fs/f2fs/dir.c @@ -1069,24 +1069,27 @@ static int f2fs_d_compare(const struct d const char *str, const struct qstr *name) { struct qstr qstr = {.name = str, .len = len }; + const struct dentry *parent = READ_ONCE(dentry->d_parent); + const struct inode *inode = READ_ONCE(parent->d_inode); - if (!IS_CASEFOLDED(dentry->d_parent->d_inode)) { + if (!inode || !IS_CASEFOLDED(inode)) { if (len != name->len) return -1; return memcmp(str, name->name, len); } - return f2fs_ci_compare(dentry->d_parent->d_inode, name, &qstr, false); + return f2fs_ci_compare(inode, name, &qstr, false); } static int f2fs_d_hash(const struct dentry *dentry, struct qstr *str) { struct f2fs_sb_info *sbi = F2FS_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)) + if (!inode || !IS_CASEFOLDED(inode)) return 0; norm = f2fs_kmalloc(sbi, PATH_MAX, GFP_ATOMIC); Patches currently in stable-queue which might be from ebiggers@xxxxxxxxxx are queue-5.5/f2fs-fix-dcache-lookup-of-casefolded-directories.patch queue-5.5/ubifs-don-t-trigger-assertion-on-invalid-no-key-filename.patch queue-5.5/fscrypt-don-t-print-name-of-busy-file-when-removing-key.patch queue-5.5/ubifs-fix-fs_ioc_setflags-unexpectedly-clearing-encrypt-flag.patch queue-5.5/f2fs-fix-race-conditions-in-d_compare-and-d_hash.patch