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    Subject[PATCH 4.4 105/158] nfsd: Fix overflow causing non-working mounts on 1 TB machines
    Date
    [ Upstream commit 3b2d4dcf71c4a91b420f835e52ddea8192300a3b ]

    Since commit 10a68cdf10 (nfsd: fix performance-limiting session
    calculation) (Linux 5.1-rc1 and 4.19.31), shares from NFS servers with
    1 TB of memory cannot be mounted anymore. The mount just hangs on the
    client.

    The gist of commit 10a68cdf10 is the change below.

    -avail = clamp_t(int, avail, slotsize, avail/3);
    +avail = clamp_t(int, avail, slotsize, total_avail/3);

    Here are the macros.

    #define min_t(type, x, y) __careful_cmp((type)(x), (type)(y), <)
    #define clamp_t(type, val, lo, hi) min_t(type, max_t(type, val, lo), hi)

    `total_avail` is 8,434,659,328 on the 1 TB machine. `clamp_t()` casts
    the values to `int`, which for 32-bit integers can only hold values
    −2,147,483,648 (−2^31) through 2,147,483,647 (2^31 − 1).

    `avail` (in the function signature) is just 65536, so that no overflow
    was happening. Before the commit the assignment would result in 21845,
    and `num = 4`.

    When using `total_avail`, it is causing the assignment to be
    18446744072226137429 (printed as %lu), and `num` is then 4164608182.

    My next guess is, that `nfsd_drc_mem_used` is then exceeded, and the
    server thinks there is no memory available any more for this client.

    Updating the arguments of `clamp_t()` and `min_t()` to `unsigned long`
    fixes the issue.

    Now, `avail = 65536` (before commit 10a68cdf10 `avail = 21845`), but
    `num = 4` remains the same.

    Fixes: c54f24e338ed (nfsd: fix performance-limiting session calculation)
    Cc: stable@vger.kernel.org
    Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
    Signed-off-by: J. Bruce Fields <bfields@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/nfsd/nfs4state.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
    index 1e1abf1d5769..ea5cb1ba282f 100644
    --- a/fs/nfsd/nfs4state.c
    +++ b/fs/nfsd/nfs4state.c
    @@ -1400,7 +1400,7 @@ static u32 nfsd4_get_drc_mem(struct nfsd4_channel_attrs *ca)
    * Never use more than a third of the remaining memory,
    * unless it's the only way to give this client a slot:
    */
    - avail = clamp_t(int, avail, slotsize, total_avail/3);
    + avail = clamp_t(unsigned long, avail, slotsize, total_avail/3);
    num = min_t(int, num, avail / slotsize);
    nfsd_drc_mem_used += num * slotsize;
    spin_unlock(&nfsd_drc_lock);
    --
    2.20.1


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