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David Howells 4fd68a35f6 afs: Fix EOF corruption
[ Upstream commit 3f4aa981816368fe6b1d13c2bfbe76df9687e787 ]

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: 31143d5d51 ("AFS: implement basic file write support")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2020-06-24 17:50:46 +02:00
arch powerpc: Fix kernel crash in show_instructions() w/DEBUG_VIRTUAL 2020-06-24 17:50:45 +02:00
block
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drivers bcache: fix potential deadlock problem in btree_gc_coalesce 2020-06-24 17:50:45 +02:00
fs afs: Fix EOF corruption 2020-06-24 17:50:46 +02:00
include usb: host: ehci-platform: add a quirk to avoid stuck 2020-06-24 17:50:44 +02:00
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kernel tracing/probe: Fix bpf_task_fd_query() for kprobes and uprobes 2020-06-24 17:50:43 +02:00
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sound ASoC: rt5645: Add platform-data for Asus T101HA 2020-06-24 17:50:42 +02:00
tools perf stat: Fix NULL pointer dereference 2020-06-24 17:50:45 +02:00
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Linux kernel
============

There are several guides for kernel developers and users. These guides can
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In order to build the documentation, use ``make htmldocs`` or
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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
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the problems which may result by upgrading your kernel.