| Message ID | 20200416162859.26518-1-mcgrof@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | coredump: fix crash when umh is disabled | expand |
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 %e > ``` > > The 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
diff --git a/fs/coredump.c b/fs/coredump.c index f8296a82d01d..c92074fb152d 100644 --- a/fs/coredump.c +++ b/fs/coredump.c @@ -786,6 +786,14 @@ void do_coredump(const kernel_siginfo_t *siginfo) if (displaced) put_files_struct(displaced); if (!dump_interrupted()) { + /* + * umh disabled with CONFIG_STATIC_USERMODEHELPER_PATH="" would + * have this set to NULL. + */ + if (!cprm.file) { + pr_info("Core dump to |%s disabled\n", cn.corename); + goto close_fail; + } file_start_write(cprm.file); core_dumped = binfmt->core_dump(&cprm); file_end_write(cprm.file); diff --git a/kernel/umh.c b/kernel/umh.c index 7f255b5a8845..11bf5eea474c 100644 --- a/kernel/umh.c +++ b/kernel/umh.c @@ -544,6 +544,11 @@ EXPORT_SYMBOL_GPL(fork_usermode_blob); * Runs a user-space application. The application is started * asynchronously if wait is not set, and runs as a child of system workqueues. * (ie. it runs with full root capabilities and optimized affinity). + * + * Note: successful return value does not guarantee the helper was called at + * all. You can't rely on sub_info->{init,cleanup} being called even for + * UMH_WAIT_* wait modes as STATIC_USERMODEHELPER_PATH="" turns all helpers + * into a successful no-op. */ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait) {