On 11/25/25 20:20, John Johansen wrote:
On 11/25/25 07:11, Helge Deller wrote:
* John Johansen <[email protected]>:
On 11/18/25 04:49, Helge Deller wrote:
Hi Adrian,
On 11/18/25 12:43, John Paul Adrian Glaubitz wrote:
On Tue, 2025-11-18 at 12:09 +0100, Helge Deller wrote:
My patch fixed two call sites, but I suspect you see another call site which
hasn't been fixed yet.
Can you try attached patch? It might indicate the caller of the function and
maybe prints the struct name/address which isn't aligned.
Helge
diff --git a/security/apparmor/match.c b/security/apparmor/match.c
index c5a91600842a..b477430c07eb 100644
--- a/security/apparmor/match.c
+++ b/security/apparmor/match.c
@@ -313,6 +313,9 @@ struct aa_dfa *aa_dfa_unpack(void *blob, size_t size, int
flags)
if (size < sizeof(struct table_set_header))
goto fail;
+ if (WARN_ON(((unsigned long)data) & (BITS_PER_LONG/8 - 1)))
+ pr_warn("dfa blob stream %pS not aligned.\n", data);
+
if (ntohl(*(__be32 *) data) != YYTH_MAGIC)
goto fail;
Here is the relevant output with the patch applied:
[ 73.840639] ------------[ cut here ]------------
[ 73.901376] WARNING: CPU: 0 PID: 341 at security/apparmor/match.c:316
aa_dfa_unpack+0x6cc/0x720
[ 74.015867] Modules linked in: binfmt_misc evdev flash sg drm
drm_panel_orientation_quirks backlight i2c_core configfs nfnetlink autofs4 ext4
crc16 mbcache jbd2 hid_generic usbhid sr_mod hid cdrom
sd_mod ata_generic ohci_pci ehci_pci ehci_hcd ohci_hcd pata_ali libata
sym53c8xx scsi_transport_spi tg3 scsi_mod usbcore libphy scsi_common mdio_bus
usb_common
[ 74.428977] CPU: 0 UID: 0 PID: 341 Comm: apparmor_parser Not tainted
6.18.0-rc6+ #9 NONE
[ 74.536543] Call Trace:
[ 74.568561] [<0000000000434c24>] dump_stack+0x8/0x18
[ 74.633757] [<0000000000476438>] __warn+0xd8/0x100
[ 74.696664] [<00000000004296d4>] warn_slowpath_fmt+0x34/0x74
[ 74.771006] [<00000000008db28c>] aa_dfa_unpack+0x6cc/0x720
[ 74.843062] [<00000000008e643c>] unpack_pdb+0xbc/0x7e0
[ 74.910545] [<00000000008e7740>] unpack_profile+0xbe0/0x1300
[ 74.984888] [<00000000008e82e0>] aa_unpack+0xe0/0x6a0
[ 75.051226] [<00000000008e3ec4>] aa_replace_profiles+0x64/0x1160
[ 75.130144] [<00000000008d4d90>] policy_update+0xf0/0x280
[ 75.201057] [<00000000008d4fc8>] profile_replace+0xa8/0x100
[ 75.274258] [<0000000000766bd0>] vfs_write+0x90/0x420
[ 75.340594] [<00000000007670cc>] ksys_write+0x4c/0xe0
[ 75.406932] [<0000000000767174>] sys_write+0x14/0x40
[ 75.472126] [<0000000000406174>] linux_sparc_syscall+0x34/0x44
[ 75.548802] ---[ end trace 0000000000000000 ]---
[ 75.609503] dfa blob stream 0xfff0000008926b96 not aligned.
[ 75.682695] Kernel unaligned access at TPC[8db2a8] aa_dfa_unpack+0x6e8/0x720
The non-8-byte-aligned address (0xfff0000008926b96) is coming from userspace
(via the write syscall).
Some apparmor userspace tool writes into the apparmor ".replace" virtual file
with
a source address which is not correctly aligned.
the userpace buffer passed to write(2) has to be aligned? Its certainly nice if
it
is but the userspace tooling hasn't been treating it as aligned. With that said,
the dfa should be padded to be aligned. So this tripping in the dfa is a bug,
and there really should be some validation to catch it.
You should be able to debug/find the problematic code with strace from
userspace.
Maybe someone with apparmor knowledge here on the list has an idea?
This is likely an unaligned 2nd profile, being split out and loaded separately
from the rest of the container. Basically the loader for some reason (there
are a few different possible reasons) is poking into the container format and
pulling out the profile at some offset, this gets loaded to the kernel but
it would seem that its causing an issue with the dfa alignment within the
container,
which should be aligned to the original container.
Regarding this:
Kernel side, we are going to need to add some extra verification checks, it
should
be catching this, as unaligned as part of the unpack. Userspace side, we will
have
to verify my guess and fix the loader.
I wonder if loading those tables are really time critical?
no, most policy is loaded once on boot and then at package upgrades. There are
some
bits that may be loaded at application startup like, snap, libvirt, lxd,
basically
container managers might do some thing custom per container.
Its the run time we want to minimize, the cost of.
Policy already can be unaligned (the container format rework to fix this is low
priority), and is treated as untrusted. It goes through an unpack, and
translation to
machine native, with as many bounds checks, necessary transforms etc done at
unpack
time as possible, so that the run time costs can be minimized.
If not, maybe just making the kernel aware that the tables might be unaligned
can help, e.g. with the following (untested) patch.
Adrian, maybe you want to test?
------------------------
[PATCH] Allow apparmor to handle unaligned dfa tables
The dfa tables can originate from kernel or userspace and 8-byte alignment
isn't always guaranteed and as such may trigger unaligned memory accesses
on various architectures.
Work around it by using the get_unaligned_xx() helpers.
Signed-off-by: Helge Deller <[email protected]>
lgtm,
Acked-by: John Johansen <[email protected]>
I'll pull this into my tree regardless of whether it fixes the issue
for Adrian, as it definitely fixes an issue.
We can added additional patches on top s needed.
My patch does not modify the UNPACK_ARRAY() macro, which we
possibly should adjust as well.
Adrian's testing seems to trigger only a few unaligned accesses,
so maybe it's not a issue currently.
Helge
