On Wed, 26 Nov 2025 01:11:45 -0800 John Johansen <[email protected]> wrote:
> On 11/25/25 13:13, Helge Deller wrote: > > 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. > > Indeed. See the patch below. I am not surprised testing hasn't triggered this > case, but a malicious userspace could certainly construct a policy that would > trigger it. Yes it would have to be root, but I still would like to prevent > root from being able to trigger this. > > > Adrian's testing seems to trigger only a few unaligned accesses, > > so maybe it's not a issue currently. > > > I don't think the userspace compiler is generating one that is bad, but it > possible to construct one and get it to the point where it can trip in > UNPACK_ARRAY > > commit 2c87528c1e7be3976b61ac797c6c8700364c4c63 > Author: John Johansen <[email protected]> > Date: Tue Nov 25 13:59:32 2025 -0800 > > apparmor: fix unaligned memory access of UNPACK_ARRAY > > The UNPACK_ARRAY macro has the potential to have unaligned memory > access when the unpacking an unaligned profile, which is caused by > userspace splitting up a profile container before sending it to the > kernel. > > While this is corner case, policy loaded from userspace should be > treated as untrusted so ensure that userspace can not trigger an > unaligned access. > > Signed-off-by: John Johansen <[email protected]> > > diff --git a/security/apparmor/include/match.h > b/security/apparmor/include/match.h > index 1fbe82f5021b1..203f7c07529f5 100644 > --- a/security/apparmor/include/match.h > +++ b/security/apparmor/include/match.h > @@ -104,7 +104,7 @@ struct aa_dfa { > struct table_header *tables[YYTD_ID_TSIZE]; > }; > > -#define byte_to_byte(X) (X) > +#define byte_to_byte(X) *(X) Even though is is only used once that ought to be (*(X)) > > #define UNPACK_ARRAY(TABLE, BLOB, LEN, TTYPE, BTYPE, NTOHX) \ > do { \ > @@ -112,7 +112,7 @@ struct aa_dfa { > TTYPE *__t = (TTYPE *) TABLE; \ > BTYPE *__b = (BTYPE *) BLOB; \ > for (__i = 0; __i < LEN; __i++) { \ > - __t[__i] = NTOHX(__b[__i]); \ > + __t[__i] = NTOHX(&__b[__i]); \ > } \ > } while (0) > > diff --git a/security/apparmor/match.c b/security/apparmor/match.c > index 26e82ba879d44..3dcc342337aca 100644 > --- a/security/apparmor/match.c > +++ b/security/apparmor/match.c > @@ -71,10 +71,10 @@ static struct table_header *unpack_table(char *blob, > size_t bsize) > u8, u8, byte_to_byte); Is that that just memcpy() ? David > else if (th.td_flags == YYTD_DATA16) > UNPACK_ARRAY(table->td_data, blob, th.td_lolen, > - u16, __be16, be16_to_cpu); > + u16, __be16, get_unaligned_be16); > else if (th.td_flags == YYTD_DATA32) > UNPACK_ARRAY(table->td_data, blob, th.td_lolen, > - u32, __be32, be32_to_cpu); > + u32, __be32, get_unaligned_be32); > else > goto fail; > /* if table was vmalloced make sure the page tables are synced > > >
