diff mbox series

btrfs: send: fix buffer overflow detection when copying path to cache entry

Message ID ee24884b0255f717071ca932bda1ab398707d9cf.1726782272.git.fdmanana@suse.com (mailing list archive)
State New
Headers show
Series btrfs: send: fix buffer overflow detection when copying path to cache entry | expand

Commit Message

Filipe Manana Sept. 19, 2024, 9:50 p.m. UTC 
From: Filipe Manana <fdmanana@suse.com>

Starting with commit c0247d289e73 ("btrfs: send: annotate struct
name_cache_entry with __counted_by()") we annotated the variable length
array "name" from the name_cache_entry structure with __counted_by() to
improve overflow detection. However that alone was not correct, because
the length of that array does not match the "name_len" field - it matches
that plus 1 to include the nul string terminador, so that makes a
fortified kernel think there's an overflow and report a splat like this:

   Sep 15 23:32:17 sdslinux1 kernel: ------------[ cut here ]------------
   Sep 15 23:32:17 sdslinux1 kernel: strcpy: detected buffer overflow: 20
   byte write of buffer size 19
   Sep 15 23:32:17 sdslinux1 kernel: WARNING: CPU: 3 PID: 3310 at
   __fortify_report+0x45/0x50
   Sep 15 23:32:17 sdslinux1 kernel: Modules linked in: nfsd auth_rpcgss
   lockd grace nfs_acl bridge stp llc bonding tls vfat fat binfmt_misc
   snd_hda_codec_hdmi intel_rapl_msr intel_rapl_common x8
   6_pkg_temp_thermal intel_powerclamp kvm_intel iTCO_wdt intel_pmc_bxt
   spi_intel_platform kvm at24 mei_wdt spi_intel mei_pxp
   iTCO_vendor_support mei_hdcp btusb snd_hda_codec_realtek btbcm btinte
   l snd_hda_scodec_component i915 rapl iwlwifi snd_hda_codec_generic btrtl
   intel_cstate btmtk cec snd_hda_intel intel_uncore cfg80211
   snd_intel_dspcfg drm_buddy coretemp snd_intel_sdw_acpi bluet
   ooth ttm pcspkr snd_hda_codec rfkill snd_hda_core snd_hwdep intel_vbtn
   snd_pcm mei_me drm_display_helper snd_timer sparse_keymap i2c_i801 mei
   snd i2c_smbus lpc_ich soundcore cdc_mbim cdc_wdm cdc_ncm cdc_ether
   usbnet crct10dif_pclmul crc32_pclmul crc32c_intel polyval_clmulni
   polyval_generic ghash_clmulni_intel sha512_ssse3 sha256_ssse3 sha1_ssse3
   igb r8152 serio_raw i2c_algo_bit mii dca e1000e video wmi sunrpc
   Sep 15 23:32:17 sdslinux1 kernel: CPU: 3 UID: 0 PID: 3310 Comm: btrfs
   Not tainted 6.11.0-prnet #1
   Sep 15 23:32:17 sdslinux1 kernel: Hardware name: CompuLab Ltd.
   sbc-ihsw/Intense-PC2 (IPC2), BIOS IPC2_3.330.7 X64 03/15/2018
   Sep 15 23:32:17 sdslinux1 kernel: RIP: 0010:__fortify_report+0x45/0x50
   Sep 15 23:32:17 sdslinux1 kernel: Code: 48 8b 34 (...)
   Sep 15 23:32:17 sdslinux1 kernel: RSP: 0018:ffff97ebc0d6f650 EFLAGS:
   00010246
   Sep 15 23:32:17 sdslinux1 kernel: RAX: 7749924ef60fa600 RBX:
   ffff8bf5446a521a RCX: 0000000000000027
   Sep 15 23:32:17 sdslinux1 kernel: RDX: 00000000ffffdfff RSI:
   ffff97ebc0d6f548 RDI: ffff8bf84e7a1cc8
   Sep 15 23:32:17 sdslinux1 kernel: RBP: ffff8bf548574080 R08:
   ffffffffa8c40e10 R09: 0000000000005ffd
   Sep 15 23:32:17 sdslinux1 kernel: R10: 0000000000000004 R11:
   ffffffffa8c70e10 R12: ffff8bf551eef400
   Sep 15 23:32:17 sdslinux1 kernel: R13: 0000000000000000 R14:
   0000000000000013 R15: 00000000000003a8
   Sep 15 23:32:17 sdslinux1 kernel: FS:  00007fae144de8c0(0000)
   GS:ffff8bf84e780000(0000) knlGS:0000000000000000
   Sep 15 23:32:17 sdslinux1 kernel: CS:  0010 DS: 0000 ES: 0000 CR0:
   0000000080050033
   Sep 15 23:32:17 sdslinux1 kernel: CR2: 00007fae14691690 CR3:
   00000001027a2003 CR4: 00000000001706f0
   Sep 15 23:32:17 sdslinux1 kernel: Call Trace:
   Sep 15 23:32:17 sdslinux1 kernel:  <TASK>
   Sep 15 23:32:17 sdslinux1 kernel:  ? __warn+0x12a/0x1d0
   Sep 15 23:32:17 sdslinux1 kernel:  ? __fortify_report+0x45/0x50
   Sep 15 23:32:17 sdslinux1 kernel:  ? report_bug+0x154/0x1c0
   Sep 15 23:32:17 sdslinux1 kernel:  ? handle_bug+0x42/0x70
   Sep 15 23:32:17 sdslinux1 kernel:  ? exc_invalid_op+0x1a/0x50
   Sep 15 23:32:17 sdslinux1 kernel:  ? asm_exc_invalid_op+0x1a/0x20
   Sep 15 23:32:17 sdslinux1 kernel:  ? __fortify_report+0x45/0x50
   Sep 15 23:32:17 sdslinux1 kernel:  __fortify_panic+0x9/0x10
   Sep 15 23:32:17 sdslinux1 kernel: __get_cur_name_and_parent+0x3bc/0x3c0
   Sep 15 23:32:17 sdslinux1 kernel:  get_cur_path+0x207/0x3b0
   Sep 15 23:32:17 sdslinux1 kernel:  send_extent_data+0x709/0x10d0
   Sep 15 23:32:17 sdslinux1 kernel:  ? find_parent_nodes+0x22df/0x25d0
   Sep 15 23:32:17 sdslinux1 kernel:  ? mas_nomem+0x13/0x90
   Sep 15 23:32:17 sdslinux1 kernel:  ? mtree_insert_range+0xa5/0x110
   Sep 15 23:32:17 sdslinux1 kernel:  ? btrfs_lru_cache_store+0x5f/0x1e0
   Sep 15 23:32:17 sdslinux1 kernel:  ? iterate_extent_inodes+0x52d/0x5a0
   Sep 15 23:32:17 sdslinux1 kernel:  process_extent+0xa96/0x11a0
   Sep 15 23:32:17 sdslinux1 kernel:  ? __pfx_lookup_backref_cache+0x10/0x10
   Sep 15 23:32:17 sdslinux1 kernel:  ? __pfx_store_backref_cache+0x10/0x10
   Sep 15 23:32:17 sdslinux1 kernel:  ? __pfx_iterate_backrefs+0x10/0x10
   Sep 15 23:32:17 sdslinux1 kernel:  ? __pfx_check_extent_item+0x10/0x10
   Sep 15 23:32:17 sdslinux1 kernel:  changed_cb+0x6fa/0x930
   Sep 15 23:32:17 sdslinux1 kernel:  ? tree_advance+0x362/0x390
   Sep 15 23:32:17 sdslinux1 kernel:  ? memcmp_extent_buffer+0xd7/0x160
   Sep 15 23:32:17 sdslinux1 kernel:  send_subvol+0xf0a/0x1520
   Sep 15 23:32:17 sdslinux1 kernel:  btrfs_ioctl_send+0x106b/0x11d0
   Sep 15 23:32:17 sdslinux1 kernel:  ? __pfx___clone_root_cmp_sort+0x10/0x10
   Sep 15 23:32:17 sdslinux1 kernel:  _btrfs_ioctl_send+0x1ac/0x240
   Sep 15 23:32:17 sdslinux1 kernel:  btrfs_ioctl+0x75b/0x850
   Sep 15 23:32:17 sdslinux1 kernel:  __se_sys_ioctl+0xca/0x150
   Sep 15 23:32:17 sdslinux1 kernel:  do_syscall_64+0x85/0x160
   Sep 15 23:32:17 sdslinux1 kernel:  ? __count_memcg_events+0x69/0x100
   Sep 15 23:32:17 sdslinux1 kernel:  ? handle_mm_fault+0x1327/0x15c0
   Sep 15 23:32:17 sdslinux1 kernel:  ? __se_sys_rt_sigprocmask+0xf1/0x180
   Sep 15 23:32:17 sdslinux1 kernel:  ? syscall_exit_to_user_mode+0x75/0xa0
   Sep 15 23:32:17 sdslinux1 kernel:  ? do_syscall_64+0x91/0x160
   Sep 15 23:32:17 sdslinux1 kernel:  ? do_user_addr_fault+0x21d/0x630
   Sep 15 23:32:17 sdslinux1 kernel: entry_SYSCALL_64_after_hwframe+0x76/0x7e
   Sep 15 23:32:17 sdslinux1 kernel: RIP: 0033:0x7fae145eeb4f
   Sep 15 23:32:17 sdslinux1 kernel: Code: 00 48 89 (...)
   Sep 15 23:32:17 sdslinux1 kernel: RSP: 002b:00007ffdf1cb09b0 EFLAGS:
   00000246 ORIG_RAX: 0000000000000010
   Sep 15 23:32:17 sdslinux1 kernel: RAX: ffffffffffffffda RBX:
   0000000000000004 RCX: 00007fae145eeb4f
   Sep 15 23:32:17 sdslinux1 kernel: RDX: 00007ffdf1cb0ad0 RSI:
   0000000040489426 RDI: 0000000000000004
   Sep 15 23:32:17 sdslinux1 kernel: RBP: 00000000000078fe R08:
   00007fae144006c0 R09: 00007ffdf1cb0927
   Sep 15 23:32:17 sdslinux1 kernel: R10: 0000000000000008 R11:
   0000000000000246 R12: 00007ffdf1cb1ce8
   Sep 15 23:32:17 sdslinux1 kernel: R13: 0000000000000003 R14:
   000055c499fab2e0 R15: 0000000000000004
   Sep 15 23:32:17 sdslinux1 kernel:  </TASK>
   Sep 15 23:32:17 sdslinux1 kernel: ---[ end trace 0000000000000000 ]---
   Sep 15 23:32:17 sdslinux1 kernel: ------------[ cut here ]------------

Fix this by not storing the nul string terminator since we don't actually
need it for name cache entries, this way "name_len" corresponds to the
actual size of the "name" array. This requires marking the "name" array
field with __nonstring and using memcpy() instead of strcpy() as
recommended by the guidelines at:

   https://github.com/KSPP/linux/issues/90

Reported-by: David Arendt <admin@prnet.org>
Link: https://lore.kernel.org/linux-btrfs/cee4591a-3088-49ba-99b8-d86b4242b8bd@prnet.org/
Fixes: c0247d289e73 ("btrfs: send: annotate struct name_cache_entry with __counted_by()")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/send.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)
diff mbox series

Patch

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 7f48ba6c1c77..ae2872033601 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -346,8 +346,10 @@  struct name_cache_entry {
 	u64 parent_gen;
 	int ret;
 	int need_later_update;
+	/* Name length without NUL terminator. */
 	int name_len;
-	char name[] __counted_by(name_len);
+	/* Not NUL terminaed. */
+	char name[] __counted_by(name_len) __nonstring;
 };
 
 /* See the comment at lru_cache.h about struct btrfs_lru_cache_entry. */
@@ -2388,7 +2390,7 @@  static int __get_cur_name_and_parent(struct send_ctx *sctx,
 	/*
 	 * Store the result of the lookup in the name cache.
 	 */
-	nce = kmalloc(sizeof(*nce) + fs_path_len(dest) + 1, GFP_KERNEL);
+	nce = kmalloc(sizeof(*nce) + fs_path_len(dest), GFP_KERNEL);
 	if (!nce) {
 		ret = -ENOMEM;
 		goto out;
@@ -2400,7 +2402,7 @@  static int __get_cur_name_and_parent(struct send_ctx *sctx,
 	nce->parent_gen = *parent_gen;
 	nce->name_len = fs_path_len(dest);
 	nce->ret = ret;
-	strcpy(nce->name, dest->start);
+	memcpy(nce->name, dest->start, nce->name_len);
 
 	if (ino < sctx->send_progress)
 		nce->need_later_update = 0;