71 lines
2.6 KiB
Diff
71 lines
2.6 KiB
Diff
From e787b36fc8d972fa762ddc91062812c26e0331c0 Mon Sep 17 00:00:00 2001
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From: Theodore Ts'o <tytso@mit.edu>
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Date: Wed, 23 May 2018 11:31:03 -0400
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Subject: [PATCH] ext4: correctly handle a zero-length xattr with a non-zero
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e_value_offs
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Ext4 will always create ext4 extended attributes which do not have a
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value (where e_value_size is zero) with e_value_offs set to zero. In
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most places e_value_offs will not be used in a substantive way if
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e_value_size is zero.
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There was one exception to this, which is in ext4_xattr_set_entry(),
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where if there is a maliciously crafted file system where there is an
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extended attribute with e_value_offs is non-zero and e_value_size is
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0, the attempt to remove this xattr will result in a negative value
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getting passed to memmove, leading to the following sadness:
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[ 41.225365] EXT4-fs (loop0): mounted filesystem with ordered data mode. Opts: (null)
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[ 44.538641] BUG: unable to handle kernel paging request at ffff9ec9a3000000
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[ 44.538733] IP: __memmove+0x81/0x1a0
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[ 44.538755] PGD 1249bd067 P4D 1249bd067 PUD 1249c1067 PMD 80000001230000e1
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[ 44.538793] Oops: 0003 [#1] SMP PTI
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[ 44.539074] CPU: 0 PID: 1470 Comm: poc Not tainted 4.16.0-rc1+ #1
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...
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[ 44.539475] Call Trace:
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[ 44.539832] ext4_xattr_set_entry+0x9e7/0xf80
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...
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[ 44.539972] ext4_xattr_block_set+0x212/0xea0
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...
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[ 44.540041] ext4_xattr_set_handle+0x514/0x610
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[ 44.540065] ext4_xattr_set+0x7f/0x120
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[ 44.540090] __vfs_removexattr+0x4d/0x60
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[ 44.540112] vfs_removexattr+0x75/0xe0
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[ 44.540132] removexattr+0x4d/0x80
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...
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[ 44.540279] path_removexattr+0x91/0xb0
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[ 44.540300] SyS_removexattr+0xf/0x20
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[ 44.540322] do_syscall_64+0x71/0x120
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[ 44.540344] entry_SYSCALL_64_after_hwframe+0x21/0x86
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https://bugzilla.kernel.org/show_bug.cgi?id=199347
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This addresses CVE-2018-10840.
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Reported-by: "Xu, Wen" <wen.xu@gatech.edu>
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Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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Reviewed-by: Andreas Dilger <adilger@dilger.ca>
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Cc: stable@kernel.org
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Fixes: dec214d00e0d7 ("ext4: xattr inode deduplication")
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Signed-off-by: Jeremy Cline <jcline@redhat.com>
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---
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fs/ext4/xattr.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
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index 499cb4b1fbd2..fc4ced59c565 100644
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--- a/fs/ext4/xattr.c
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+++ b/fs/ext4/xattr.c
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@@ -1688,7 +1688,7 @@ static int ext4_xattr_set_entry(struct ext4_xattr_info *i,
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/* No failures allowed past this point. */
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- if (!s->not_found && here->e_value_offs) {
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+ if (!s->not_found && here->e_value_size && here->e_value_offs) {
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/* Remove the old value. */
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void *first_val = s->base + min_offs;
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size_t offs = le16_to_cpu(here->e_value_offs);
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--
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2.17.0
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