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authorTheodore Ts'o <tytso@mit.edu>2018-05-23 18:31:03 +0300
committerTheodore Ts'o <tytso@mit.edu>2018-05-23 18:31:03 +0300
commit8a2b307c21d4b290e3cbe33f768f194286d07c23 (patch)
tree6c55d0950c02c42c96be5297a2154110a48124b0
parenteb9b5f01c33adebc31cbc236c02695f605b0e417 (diff)
downloadlinux-8a2b307c21d4b290e3cbe33f768f194286d07c23.tar.xz
ext4: correctly handle a zero-length xattr with a non-zero e_value_offs
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")
-rw-r--r--fs/ext4/xattr.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 499cb4b1fbd2..fc4ced59c565 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1688,7 +1688,7 @@ static int ext4_xattr_set_entry(struct ext4_xattr_info *i,
/* 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);