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authorRoland Dreier <rolandd@cisco.com>2008-06-06 21:38:37 -0700
committerRoland Dreier <rolandd@cisco.com>2008-06-06 21:38:37 -0700
commit8079ffa0e18baaf2940e52e0c118eef420a473a4 (patch)
tree9593f8c324864bcb8514548d3ecab7cc1bf1cab7 /include/rdma
parentaab2545fdd6641b76af0ae96456c4ca9d1e50dad (diff)
IB/umem: Avoid sign problems when demoting npages to integer
On a 64-bit architecture, if ib_umem_get() is called with a size value that is so big that npages is negative when cast to int, then the length of the page list passed to get_user_pages(), namely min_t(int, npages, PAGE_SIZE / sizeof (struct page *)) will be negative, and get_user_pages() will immediately return 0 (at least since 900cf086, "Be more robust about bad arguments in get_user_pages()"). This leads to an infinite loop in ib_umem_get(), since the code boils down to: while (npages) { ret = get_user_pages(...); npages -= ret; } Fix this by taking the minimum as unsigned longs, so that the value of npages is never truncated. The impact of this bug isn't too severe, since the value of npages is checked against RLIMIT_MEMLOCK, so a process would need to have an astronomical limit or have CAP_IPC_LOCK to be able to trigger this, and such a process could already cause lots of mischief. But it does let buggy userspace code cause a kernel lock-up; for example I hit this with code that passes a negative value into a memory registartion function where it is promoted to a huge u64 value. Cc: <stable@kernel.org> Signed-off-by: Roland Dreier <rolandd@cisco.com>
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