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fs/binfmt_misc.c: do not allow offset overflow
commit 5cc41e0 upstream. 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. 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. Link: http://lkml.kernel.org/r/[email protected] Fixes: 1da177e ("Linux-2.6.12-rc2") Signed-off-by: Thadeu Lima de Souza Cascardo <[email protected]> Reviewed-by: Andrew Morton <[email protected]> Cc: Alexander Viro <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> [bwh: Backported to 3.16: - Error label is "Einval" - Adjust context] Signed-off-by: Ben Hutchings <[email protected]>
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