On Thu, Mar 04, 2021 at 11:51:26AM +0530, Ritesh Harjani wrote: > In case if isi.nr_pages is 0, we are making sis->pages (which is > unsigned int) a huge value in iomap_swapfile_activate() by assigning -1. > This could cause a kernel crash in kernel v4.18 (with below signature). > Or could lead to unknown issues on latest kernel if the fake big swap gets > used. > > Fix this issue by returning -EINVAL in case of nr_pages is 0, since it > is anyway a invalid swapfile. Looks like this issue will be hit when > we have pagesize < blocksize type of configuration. > > I was able to hit the issue in case of a tiny swap file with below > test script. > https://raw.githubusercontent.com/riteshharjani/LinuxStudy/master/scripts/swap-issue.sh Can you turn this into a dangerous-group fstest, please? > kernel crash analysis on v4.18 > ============================== > On v4.18 kernel, it causes a kernel panic, since sis->pages becomes > a huge value and isi.nr_extents is 0. When 0 is returned it is > considered as a swapfile over NFS and SWP_FILE is set (sis->flags |= SWP_FILE). > Then when swapoff was getting called it was calling a_ops->swap_deactivate() > if (sis->flags & SWP_FILE) is true. Since a_ops->swap_deactivate() is > NULL in case of XFS, it causes below panic. Does the same reasoning apply to upstream? > Panic signature on v4.18 kernel: > ======================================= > root@qemu:/home/qemu# [ 8291.723351] XFS (loop2): Unmounting Filesystem > [ 8292.123104] XFS (loop2): Mounting V5 Filesystem > [ 8292.132451] XFS (loop2): Ending clean mount > [ 8292.263362] Adding 4294967232k swap on /mnt1/test/swapfile. Priority:-2 extents:1 across:274877906880k > [ 8292.277834] Unable to handle kernel paging request for instruction fetch > [ 8292.278677] Faulting instruction address: 0x00000000 > cpu 0x19: Vector: 400 (Instruction Access) at [c0000009dd5b7ad0] > pc: 0000000000000000 > lr: c0000000003eb9dc: destroy_swap_extents+0xfc/0x120 > sp: c0000009dd5b7d50 > msr: 8000000040009033 > current = 0xc0000009b6710080 > paca = 0xc00000003ffcb280 irqmask: 0x03 irq_happened: 0x01 > pid = 5604, comm = swapoff > Linux version 4.18.0 (riteshh@xxxxxxx) (gcc version 8.4.0 (Ubuntu 8.4.0-1ubuntu1~18.04)) #57 SMP Wed Mar 3 01:33:04 CST 2021 > enter ? for help > [link register ] c0000000003eb9dc destroy_swap_extents+0xfc/0x120 > [c0000009dd5b7d50] c0000000025a7058 proc_poll_event+0x0/0x4 (unreliable) > [c0000009dd5b7da0] c0000000003f0498 sys_swapoff+0x3f8/0x910 > [c0000009dd5b7e30] c00000000000bbe4 system_call+0x5c/0x70 > --- Exception: c01 (System Call) at 00007ffff7d208d8 > > Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx> > --- > fs/iomap/swapfile.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/fs/iomap/swapfile.c b/fs/iomap/swapfile.c > index a648dbf6991e..67953678c99f 100644 > --- a/fs/iomap/swapfile.c > +++ b/fs/iomap/swapfile.c > @@ -170,6 +170,15 @@ int iomap_swapfile_activate(struct swap_info_struct *sis, > return ret; > } > > + /* > + * In case if nr_pages is 0 then we better return -EINVAL > + * since it is anyway an empty swapfile. > + */ > + if (isi.nr_pages == 0) { > + pr_warn("swapon: Empty swap-file\n"); The swapfile might not be empty, it's just that we couldn't find even a single page's worth of contiguous space in the whole file. I would suggest: /* * If this swapfile doesn't contain even a single page-aligned * contiguous range of blocks, reject this useless swapfile to * prevent confusion later on. */ if (isi.nr_pages == 0) { pr_warn("swapon: Cannot find a single usable page in file.\n"); return -EINVAL; } --D > + return -EINVAL; > + } > + > *pagespan = 1 + isi.highest_ppage - isi.lowest_ppage; > sis->max = isi.nr_pages; > sis->pages = isi.nr_pages - 1; > -- > 2.26.2 >
