This is a note to let you know that I've just added the patch titled
capabilities: fix buffer overread on very short xattr
to the 4.14-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:
capabilities-fix-buffer-overread-on-very-short-xattr.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From dc32b5c3e6e2ef29cef76d9ce1b92d394446150e Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@xxxxxxxxxx>
Date: Mon, 1 Jan 2018 09:28:31 -0600
Subject: capabilities: fix buffer overread on very short xattr
From: Eric Biggers <ebiggers@xxxxxxxxxx>
commit dc32b5c3e6e2ef29cef76d9ce1b92d394446150e upstream.
If userspace attempted to set a "security.capability" xattr shorter than
4 bytes (e.g. 'setfattr -n security.capability -v x file'), then
cap_convert_nscap() read past the end of the buffer containing the xattr
value because it accessed the ->magic_etc field without verifying that
the xattr value is long enough to contain that field.
Fix it by validating the xattr value size first.
This bug was found using syzkaller with KASAN. The KASAN report was as
follows (cleaned up slightly):
BUG: KASAN: slab-out-of-bounds in cap_convert_nscap+0x514/0x630 security/commoncap.c:498
Read of size 4 at addr ffff88002d8741c0 by task syz-executor1/2852
CPU: 0 PID: 2852 Comm: syz-executor1 Not tainted 4.15.0-rc6-00200-gcc0aac99d977 #253
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-20171110_100015-anatol 04/01/2014
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0xe3/0x195 lib/dump_stack.c:53
print_address_description+0x73/0x260 mm/kasan/report.c:252
kasan_report_error mm/kasan/report.c:351 [inline]
kasan_report+0x235/0x350 mm/kasan/report.c:409
cap_convert_nscap+0x514/0x630 security/commoncap.c:498
setxattr+0x2bd/0x350 fs/xattr.c:446
path_setxattr+0x168/0x1b0 fs/xattr.c:472
SYSC_setxattr fs/xattr.c:487 [inline]
SyS_setxattr+0x36/0x50 fs/xattr.c:483
entry_SYSCALL_64_fastpath+0x18/0x85
Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities")
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Reviewed-by: Serge Hallyn <serge@xxxxxxxxxx>
Signed-off-by: James Morris <james.l.morris@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
security/commoncap.c | 21 +++++++++------------
1 file changed, 9 insertions(+), 12 deletions(-)
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -348,21 +348,18 @@ static __u32 sansflags(__u32 m)
return m & ~VFS_CAP_FLAGS_EFFECTIVE;
}
-static bool is_v2header(size_t size, __le32 magic)
+static bool is_v2header(size_t size, const struct vfs_cap_data *cap)
{
- __u32 m = le32_to_cpu(magic);
if (size != XATTR_CAPS_SZ_2)
return false;
- return sansflags(m) == VFS_CAP_REVISION_2;
+ return sansflags(le32_to_cpu(cap->magic_etc)) == VFS_CAP_REVISION_2;
}
-static bool is_v3header(size_t size, __le32 magic)
+static bool is_v3header(size_t size, const struct vfs_cap_data *cap)
{
- __u32 m = le32_to_cpu(magic);
-
if (size != XATTR_CAPS_SZ_3)
return false;
- return sansflags(m) == VFS_CAP_REVISION_3;
+ return sansflags(le32_to_cpu(cap->magic_etc)) == VFS_CAP_REVISION_3;
}
/*
@@ -405,7 +402,7 @@ int cap_inode_getsecurity(struct inode *
fs_ns = inode->i_sb->s_user_ns;
cap = (struct vfs_cap_data *) tmpbuf;
- if (is_v2header((size_t) ret, cap->magic_etc)) {
+ if (is_v2header((size_t) ret, cap)) {
/* If this is sizeof(vfs_cap_data) then we're ok with the
* on-disk value, so return that. */
if (alloc)
@@ -413,7 +410,7 @@ int cap_inode_getsecurity(struct inode *
else
kfree(tmpbuf);
return ret;
- } else if (!is_v3header((size_t) ret, cap->magic_etc)) {
+ } else if (!is_v3header((size_t) ret, cap)) {
kfree(tmpbuf);
return -EINVAL;
}
@@ -470,9 +467,9 @@ static kuid_t rootid_from_xattr(const vo
return make_kuid(task_ns, rootid);
}
-static bool validheader(size_t size, __le32 magic)
+static bool validheader(size_t size, const struct vfs_cap_data *cap)
{
- return is_v2header(size, magic) || is_v3header(size, magic);
+ return is_v2header(size, cap) || is_v3header(size, cap);
}
/*
@@ -495,7 +492,7 @@ int cap_convert_nscap(struct dentry *den
if (!*ivalue)
return -EINVAL;
- if (!validheader(size, cap->magic_etc))
+ if (!validheader(size, cap))
return -EINVAL;
if (!capable_wrt_inode_uidgid(inode, CAP_SETFCAP))
return -EPERM;
Patches currently in stable-queue which might be from ebiggers@xxxxxxxxxx are
queue-4.14/capabilities-fix-buffer-overread-on-very-short-xattr.patch