On Thu, Apr 16, 2020 at 04:28:59PM +0000, Luis R. Rodriguez wrote:
From: Luis Chamberlain mcgrof@kernel.org
Commit 64e90a8acb859 ("Introduce STATIC_USERMODEHELPER to mediate call_usermodehelper()") added the optiont to disable all call_usermodehelper() calls by setting STATIC_USERMODEHELPER_PATH to an empty string. When this is done, and crashdump is triggered, it will crash on null pointer dereference, since we make assumptions over what call_usermodehelper_exec() did.
This has been reported by Sergey when one triggers a a coredump with the following configuration:
CONFIG_STATIC_USERMODEHELPER=y CONFIG_STATIC_USERMODEHELPER_PATH="" kernel.core_pattern = |/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h %eThe way disabling the umh was designed was that call_usermodehelper_exec() would just return early, without an error. But coredump assumes certain variables are set up for us when this happens, and calls ile_start_write(cprm.file) with a NULL file.
[ 2.819676] BUG: kernel NULL pointer dereference, address: 0000000000000020 [ 2.819859] #PF: supervisor read access in kernel mode [ 2.820035] #PF: error_code(0x0000) - not-present page [ 2.820188] PGD 0 P4D 0 [ 2.820305] Oops: 0000 [#1] SMP PTI [ 2.820436] CPU: 2 PID: 89 Comm: a Not tainted 5.7.0-rc1+ #7 [ 2.820680] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190711_202441-buildvm-armv7-10.arm.fedoraproject.org-2.fc31 04/01/2014 [ 2.821150] RIP: 0010:do_coredump+0xd80/0x1060 [ 2.821385] Code: e8 95 11 ed ff 48 c7 c6 cc a7 b4 81 48 8d bd 28 ff ff ff 89 c2 e8 70 f1 ff ff 41 89 c2 85 c0 0f 84 72 f7 ff ff e9 b4 fe ff ff <48> 8b 57 20 0f b7 02 66 25 00 f0 66 3d 00 8 0 0f 84 9c 01 00 00 44 [ 2.822014] RSP: 0000:ffffc9000029bcb8 EFLAGS: 00010246 [ 2.822339] RAX: 0000000000000000 RBX: ffff88803f860000 RCX: 000000000000000a [ 2.822746] RDX: 0000000000000009 RSI: 0000000000000282 RDI: 0000000000000000 [ 2.823141] RBP: ffffc9000029bde8 R08: 0000000000000000 R09: ffffc9000029bc00 [ 2.823508] R10: 0000000000000001 R11: ffff88803dec90be R12: ffffffff81c39da0 [ 2.823902] R13: ffff88803de84400 R14: 0000000000000000 R15: 0000000000000000 [ 2.824285] FS: 00007fee08183540(0000) GS:ffff88803e480000(0000) knlGS:0000000000000000 [ 2.824767] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 2.825111] CR2: 0000000000000020 CR3: 000000003f856005 CR4: 0000000000060ea0 [ 2.825479] Call Trace: [ 2.825790] get_signal+0x11e/0x720 [ 2.826087] do_signal+0x1d/0x670 [ 2.826361] ? force_sig_info_to_task+0xc1/0xf0 [ 2.826691] ? force_sig_fault+0x3c/0x40 [ 2.826996] ? do_trap+0xc9/0x100 [ 2.827179] exit_to_usermode_loop+0x49/0x90 [ 2.827359] prepare_exit_to_usermode+0x77/0xb0 [ 2.827559] ? invalid_op+0xa/0x30 [ 2.827747] ret_from_intr+0x20/0x20 [ 2.827921] RIP: 0033:0x55e2c76d2129 [ 2.828107] Code: 2d ff ff ff e8 68 ff ff ff 5d c6 05 18 2f 00 00 01 c3 0f 1f 80 00 00 00 00 c3 0f 1f 80 00 00 00 00 e9 7b ff ff ff 55 48 89 e5 <0f> 0b b8 00 00 00 00 5d c3 66 2e 0f 1f 84 0 0 00 00 00 00 0f 1f 40 [ 2.828603] RSP: 002b:00007fffeba5e080 EFLAGS: 00010246 [ 2.828801] RAX: 000055e2c76d2125 RBX: 0000000000000000 RCX: 00007fee0817c718 [ 2.829034] RDX: 00007fffeba5e188 RSI: 00007fffeba5e178 RDI: 0000000000000001 [ 2.829257] RBP: 00007fffeba5e080 R08: 0000000000000000 R09: 00007fee08193c00 [ 2.829482] R10: 0000000000000009 R11: 0000000000000000 R12: 000055e2c76d2040 [ 2.829727] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 [ 2.829964] CR2: 0000000000000020 [ 2.830149] ---[ end trace ceed83d8c68a1bf1 ]---
Cc: <stable@vger.kernel.org> # v4.11+ Fixes: 64e90a8acb859 ("Introduce STATIC_USERMODEHELPER to mediate call_usermodehelper()")
Nit, you don't need so many digits, it should be: Fixes: 64e90a8acb85 ("Introduce STATIC_USERMODEHELPER to mediate call_usermodehelper()")
BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=199795 Reported-by: Tony Vroon chainsaw@gentoo.org Reported-by: Sergey Kvachonok ravenexp@gmail.com Tested-by: Sergei Trofimovich slyfox@gentoo.org Signed-off-by: Luis Chamberlain mcgrof@kernel.org
fs/coredump.c | 8 ++++++++ kernel/umh.c | 5 +++++ 2 files changed, 13 insertions(+)
Anyway, I can take this in my driver core tree if no one else objects.
thanks,
greg k-h