4.17-stable review patch. If anyone has any objections, please let me know.
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From: Theodore Ts'o tytso@mit.edu
commit 8a2b307c21d4b290e3cbe33f768f194286d07c23 upstream.
Ext4 will always create ext4 extended attributes which do not have a value (where e_value_size is zero) with e_value_offs set to zero. In most places e_value_offs will not be used in a substantive way if e_value_size is zero.
There was one exception to this, which is in ext4_xattr_set_entry(), where if there is a maliciously crafted file system where there is an extended attribute with e_value_offs is non-zero and e_value_size is 0, the attempt to remove this xattr will result in a negative value getting passed to memmove, leading to the following sadness:
[ 41.225365] EXT4-fs (loop0): mounted filesystem with ordered data mode. Opts: (null) [ 44.538641] BUG: unable to handle kernel paging request at ffff9ec9a3000000 [ 44.538733] IP: __memmove+0x81/0x1a0 [ 44.538755] PGD 1249bd067 P4D 1249bd067 PUD 1249c1067 PMD 80000001230000e1 [ 44.538793] Oops: 0003 [#1] SMP PTI [ 44.539074] CPU: 0 PID: 1470 Comm: poc Not tainted 4.16.0-rc1+ #1 ... [ 44.539475] Call Trace: [ 44.539832] ext4_xattr_set_entry+0x9e7/0xf80 ... [ 44.539972] ext4_xattr_block_set+0x212/0xea0 ... [ 44.540041] ext4_xattr_set_handle+0x514/0x610 [ 44.540065] ext4_xattr_set+0x7f/0x120 [ 44.540090] __vfs_removexattr+0x4d/0x60 [ 44.540112] vfs_removexattr+0x75/0xe0 [ 44.540132] removexattr+0x4d/0x80 ... [ 44.540279] path_removexattr+0x91/0xb0 [ 44.540300] SyS_removexattr+0xf/0x20 [ 44.540322] do_syscall_64+0x71/0x120 [ 44.540344] entry_SYSCALL_64_after_hwframe+0x21/0x86
https://bugzilla.kernel.org/show_bug.cgi?id=199347
This addresses CVE-2018-10840.
Reported-by: "Xu, Wen" wen.xu@gatech.edu Signed-off-by: Theodore Ts'o tytso@mit.edu Reviewed-by: Andreas Dilger adilger@dilger.ca Cc: stable@kernel.org Fixes: dec214d00e0d7 ("ext4: xattr inode deduplication") Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/ext4/xattr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -1688,7 +1688,7 @@ static int ext4_xattr_set_entry(struct e
/* No failures allowed past this point. */
- if (!s->not_found && here->e_value_offs) { + if (!s->not_found && here->e_value_size && here->e_value_offs) { /* Remove the old value. */ void *first_val = s->base + min_offs; size_t offs = le16_to_cpu(here->e_value_offs);