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fs: fix fd table size alignment properly

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[ Upstream commit d888c83fcec75194a8a48ccd283953bdba7b2550 ]

Jason Donenfeld reports that my commit 1c24a186398f ("fs: fd tables have
to be multiples of BITS_PER_LONG") doesn't work, and the reason is an
embarrassing brown-paper-bag bug.

Yes, we want to align the number of fds to BITS_PER_LONG, and yes, the
reason they might not be aligned is because the incoming 'max_fd'
argument might not be aligned.

But aligining the argument - while simple - will cause a "infinitely
big" maxfd (eg NR_OPEN_MAX) to just overflow to zero.  Which most
definitely isn't what we want either.

The obvious fix was always just to do the alignment last, but I had
moved it earlier just to make the patch smaller and the code look
simpler.  Duh.  It certainly made _me_ look simple.

Fixes: 1c24a186398f ("fs: fd tables have to be multiples of BITS_PER_LONG")
Reported-and-tested-by: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Fedor Pchelkin <aissur0002@gmail.com>
Cc: Alexey Khoroshilov <khoroshilov@ispras.ru>
Cc: Christian Brauner <brauner@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Linus Torvalds
2022-03-29 23:29:18 -07:00
committed by Greg Kroah-Hartman
parent 327f07e370
commit e600b5973e
1 changed files with 1 additions and 2 deletions
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3
fs/file.c
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@@ -301,10 +301,9 @@ static unsigned int sane_fdtable_size(struct fdtable *fdt, unsigned int max_fds)
unsigned int count; unsigned int count;
count = count_open_files(fdt); count = count_open_files(fdt);
max_fds = ALIGN(max_fds, BITS_PER_LONG);
if (max_fds < NR_OPEN_DEFAULT) if (max_fds < NR_OPEN_DEFAULT)
max_fds = NR_OPEN_DEFAULT; max_fds = NR_OPEN_DEFAULT;
return min(count, max_fds); return ALIGN(min(count, max_fds), BITS_PER_LONG);
} }
/* /*