A length within a page of ULONG_MAX wraps when mlock() and munlock() round the range to pages. At an aligned address the length becomes 0 and the call is a silent success; at an unaligned one it becomes a single page, which is then locked or unlocked. An overflowing start + len is only caught in apply_vma_lock_flags(), after the RLIMIT_MEMLOCK check, so mlock() returns -ENOMEM without CAP_IPC_LOCK and -EINVAL with it.
Return -EINVAL, as man 2 mlock documents, when start + len overflows or the end overflows when rounded up to a page. Doing this before can_do_mlock() also avoids making the result depend on RLIMIT_MEMLOCK/CAP_IPC_LOCK. Requests that get a silent success today now fail. Reported-by: Park Tae-sun <[email protected]> Closes: https://lore.kernel.org/all/[email protected]/ Signed-off-by: Jose A. Perez de Azpillaga <[email protected]> --- mm/mlock.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/mm/mlock.c b/mm/mlock.c index cc28e5d7413a..a9e2b90c058f 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -608,6 +608,7 @@ static __must_check int do_mlock(unsigned long start, size_t len, { unsigned long locked; unsigned long lock_limit; + unsigned long end; int error = -ENOMEM; start = untagged_addr(start); @@ -615,12 +616,19 @@ static __must_check int do_mlock(unsigned long start, size_t len, if (!len) return 0; + /* Reject a wrapping range before can_do_mlock() and the rlimit check. */ + end = start + len; + if (end < start) + return -EINVAL; + end = PAGE_ALIGN(end); + if (!end) + return -EINVAL; + start &= PAGE_MASK; + len = end - start; + if (!can_do_mlock()) return -EPERM; - len = PAGE_ALIGN(len + (offset_in_page(start))); - start &= PAGE_MASK; - lock_limit = rlimit(RLIMIT_MEMLOCK); lock_limit >>= PAGE_SHIFT; locked = len >> PAGE_SHIFT; @@ -676,6 +684,7 @@ SYSCALL_DEFINE3(mlock2, unsigned long, start, size_t, len, int, flags) SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len) { + unsigned long end; vma_flags_t flags = EMPTY_VMA_FLAGS; int ret; @@ -684,8 +693,14 @@ SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len) if (!len) return 0; - len = PAGE_ALIGN(len + (offset_in_page(start))); + end = start + len; + if (end < start) + return -EINVAL; + end = PAGE_ALIGN(end); + if (!end) + return -EINVAL; start &= PAGE_MASK; + len = end - start; if (mmap_write_lock_killable(current->mm)) return -EINTR; -- 2.55.0
