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author | David Howells <dhowells@redhat.com> | 2020-06-13 02:03:48 +0300 |
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committer | David Howells <dhowells@redhat.com> | 2020-06-15 17:41:02 +0300 |
commit | 3f4aa981816368fe6b1d13c2bfbe76df9687e787 (patch) | |
tree | 3bc76d1b3df9b0dd3834be4ed4751e443deae20c /fs/afs/dir.c | |
parent | 1f32ef79897052ef7d3d154610d8d6af95abde83 (diff) | |
download | linux-3f4aa981816368fe6b1d13c2bfbe76df9687e787.tar.xz |
afs: Fix EOF corruption
When doing a partial writeback, afs_write_back_from_locked_page() may
generate an FS.StoreData RPC request that writes out part of a file when a
file has been constructed from pieces by doing seek, write, seek, write,
... as is done by ld.
The FS.StoreData RPC is given the current i_size as the file length, but
the server basically ignores it unless the data length is 0 (in which case
it's just a truncate operation). The revised file length returned in the
result of the RPC may then not reflect what we suggested - and this leads
to i_size getting moved backwards - which causes issues later.
Fix the client to take account of this by ignoring the returned file size
unless the data version number jumped unexpectedly - in which case we're
going to have to clear the pagecache and reload anyway.
This can be observed when doing a kernel build on an AFS mount. The
following pair of commands produce the issue:
ld -m elf_x86_64 -z max-page-size=0x200000 --emit-relocs \
-T arch/x86/realmode/rm/realmode.lds \
arch/x86/realmode/rm/header.o \
arch/x86/realmode/rm/trampoline_64.o \
arch/x86/realmode/rm/stack.o \
arch/x86/realmode/rm/reboot.o \
-o arch/x86/realmode/rm/realmode.elf
arch/x86/tools/relocs --realmode \
arch/x86/realmode/rm/realmode.elf \
>arch/x86/realmode/rm/realmode.relocs
This results in the latter giving:
Cannot read ELF section headers 0/18: Success
as the realmode.elf file got corrupted.
The sequence of events can also be driven with:
xfs_io -t -f \
-c "pwrite -S 0x58 0 0x58" \
-c "pwrite -S 0x59 10000 1000" \
-c "close" \
/afs/example.com/scratch/a
Fixes: 31143d5d515e ("AFS: implement basic file write support")
Signed-off-by: David Howells <dhowells@redhat.com>
Diffstat (limited to 'fs/afs/dir.c')
0 files changed, 0 insertions, 0 deletions