Public bug reported:
[Impact]
When registering a new binfmt_misc handler, it is possible to overflow
the offset to get a negative value, which might crash the system, or
possibly leak kernel data.
Here is a crash log when 2500000000 was used as an offset:
BUG: unable to handle kernel paging request at ffff989cfd6edca0
IP: load_misc_binary+0x22b/0x470 [binfmt_misc]
PGD 1ef3e067 P4D 1ef3e067 PUD 0
Oops: 0000 [#1] SMP NOPTI
Modules linked in: binfmt_misc kvm_intel ppdev kvm irqbypass joydev
input_leds serio_raw mac_hid parport_pc qemu_fw_cfg parpy
CPU: 0 PID: 2499 Comm: bash Not tainted 4.15.0-22-generic #24-Ubuntu
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.1-1
04/01/2014
RIP: 0010:load_misc_binary+0x22b/0x470 [binfmt_misc]
Call Trace:
search_binary_handler+0x97/0x1d0
do_execveat_common.isra.34+0x667/0x810
SyS_execve+0x31/0x40
do_syscall_64+0x73/0x130
entry_SYSCALL_64_after_hwframe+0x3d/0xa2
Use kstrtoint instead of simple_strtoul. It will work as the code
already set the delimiter byte to '\0' and we only do it when the field
is not empty.
[Test Case]
Tested with offsets -1, 2500000000, UINT_MAX and INT_MAX. Also tested
with examples documented at Documentation/admin-guide/binfmt-misc.rst
and other registrations from packages on Ubuntu.
[Regression]
Fail to register valid types. This was tested with a bionic kernel with the
patch.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1775856
Title:
register on binfmt_misc may overflow and crash the system
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