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When the max pages (last_page in the swap header + 1) is smaller than the total pages (inode size) of the swapfile, iomap_swapfile_activate overwrites sis->max with total pages. However, frontswap_map is a swap page state bitmap allocated using the initial sis->max page count read from the swap header. If swapfile activation increases sis->max, it's possible for the frontswap code to walk off the end of the bitmap, thereby corrupting kernel memory. [djwong: modify the description a bit; the original paragraph reads: "However, frontswap_map is allocated using max pages. When test and clear the sis offset, which is larger than max pages, of frontswap_map in __frontswap_invalidate_page(), neighbors of frontswap_map may be overwritten, i.e., slab is polluted." Note also that this bug resulted in a behavioral change: activating a swap file that was formatted and later extended results in all pages being activated, not the number of pages recorded in the swap header.] This fixes the issue by considering the limitation of max pages of swap info in iomap_swapfile_add_extent(). To reproduce the case, compile kernel with slub RED ZONE, then run test: $ sudo stress-ng -a 1 -x softlockup,resources -t 72h --metrics --times \ --verify -v -Y /root/tmpdir/stress-ng/stress-statistic-12.yaml \ --log-file /root/tmpdir/stress-ng/stress-logfile-12.txt \ --temp-path /root/tmpdir/stress-ng/ We'll get the error log as below: [ 1151.015141] ============================================================================= [ 1151.016489] BUG kmalloc-16 (Not tainted): Right Redzone overwritten [ 1151.017486] ----------------------------------------------------------------------------- [ 1151.017486] [ 1151.018997] Disabling lock debugging due to kernel taint [ 1151.019873] INFO: 0x0000000084e43932-0x0000000098d17cae @offset=7392. First byte 0x0 instead of 0xcc [ 1151.021303] INFO: Allocated in __do_sys_swapon+0xcf6/0x1170 age=43417 cpu=9 pid=3816 [ 1151.022538] __slab_alloc+0xe/0x20 [ 1151.023069] __kmalloc_node+0xfd/0x4b0 [ 1151.023704] __do_sys_swapon+0xcf6/0x1170 [ 1151.024346] do_syscall_64+0x33/0x40 [ 1151.024925] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 1151.025749] INFO: Freed in put_cred_rcu+0xa1/0xc0 age=43424 cpu=3 pid=2041 [ 1151.026889] kfree+0x276/0x2b0 [ 1151.027405] put_cred_rcu+0xa1/0xc0 [ 1151.027949] rcu_do_batch+0x17d/0x410 [ 1151.028566] rcu_core+0x14e/0x2b0 [ 1151.029084] __do_softirq+0x101/0x29e [ 1151.029645] asm_call_irq_on_stack+0x12/0x20 [ 1151.030381] do_softirq_own_stack+0x37/0x40 [ 1151.031037] do_softirq.part.15+0x2b/0x30 [ 1151.031710] __local_bh_enable_ip+0x4b/0x50 [ 1151.032412] copy_fpstate_to_sigframe+0x111/0x360 [ 1151.033197] __setup_rt_frame+0xce/0x480 [ 1151.033809] arch_do_signal+0x1a3/0x250 [ 1151.034463] exit_to_user_mode_prepare+0xcf/0x110 [ 1151.035242] syscall_exit_to_user_mode+0x27/0x190 [ 1151.035970] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 1151.036795] INFO: Slab 0x000000003b9de4dc objects=44 used=9 fp=0x00000000539e349e flags=0xfffffc0010201 [ 1151.038323] INFO: Object 0x000000004855ba01 @offset=7376 fp=0x0000000000000000 [ 1151.038323] [ 1151.039683] Redzone 000000008d0afd3d: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc ................ [ 1151.041180] Object 000000004855ba01: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ [ 1151.042714] Redzone 0000000084e43932: 00 00 00 c0 cc cc cc cc ........ [ 1151.044120] Padding 000000000864c042: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZZZZZ [ 1151.045615] CPU: 5 PID: 3816 Comm: stress-ng Tainted: G B 5.10.50+ #7 [ 1151.046846] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014 [ 1151.048633] Call Trace: [ 1151.049072] dump_stack+0x57/0x6a [ 1151.049585] check_bytes_and_report+0xed/0x110 [ 1151.050320] check_object+0x1eb/0x290 [ 1151.050924] ? __x64_sys_swapoff+0x39a/0x540 [ 1151.051646] free_debug_processing+0x151/0x350 [ 1151.052333] __slab_free+0x21a/0x3a0 [ 1151.052938] ? _cond_resched+0x2d/0x40 [ 1151.053529] ? __vunmap+0x1de/0x220 [ 1151.054139] ? __x64_sys_swapoff+0x39a/0x540 [ 1151.054796] ? kfree+0x276/0x2b0 [ 1151.055307] kfree+0x276/0x2b0 [ 1151.055832] __x64_sys_swapoff+0x39a/0x540 [ 1151.056466] do_syscall_64+0x33/0x40 [ 1151.057084] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 1151.057866] RIP: 0033:0x150340b0ffb7 [ 1151.058481] Code: Unable to access opcode bytes at RIP 0x150340b0ff8d. [ 1151.059537] RSP: 002b:00007fff7f4ee238 EFLAGS: 00000246 ORIG_RAX: 00000000000000a8 [ 1151.060768] RAX: ffffffffffffffda RBX: 00007fff7f4ee66c RCX: 0000150340b0ffb7 [ 1151.061904] RDX: 000000000000000a RSI: 0000000000018094 RDI: 00007fff7f4ee860 [ 1151.063033] RBP: 00007fff7f4ef980 R08: 0000000000000000 R09: 0000150340a672bd [ 1151.064135] R10: 00007fff7f4edca0 R11: 0000000000000246 R12: 0000000000018094 [ 1151.065253] R13: 0000000000000005 R14: 000000000160d930 R15: 00007fff7f4ee66c [ 1151.066413] FIX kmalloc-16: Restoring 0x0000000084e43932-0x0000000098d17cae=0xcc [ 1151.066413] [ 1151.067890] FIX kmalloc-16: Object at 0x000000004855ba01 not freed Fixes: |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.