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author | Heiko Carstens <heiko.carstens@de.ibm.com> | 2018-02-07 00:37:13 +0100 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-02-07 03:32:43 +0100 |
commit | d0290bc20d4739b7a900ae37eb5d4cc3be2b393f (patch) | |
tree | f5b70cc2b188c70c2b5628fa71b51cc9dbe4dfcd /fs | |
parent | fs/proc/array.c: delete children_seq_release() (diff) | |
download | linux-d0290bc20d4739b7a900ae37eb5d4cc3be2b393f.tar.xz linux-d0290bc20d4739b7a900ae37eb5d4cc3be2b393f.zip |
fs/proc/kcore.c: use probe_kernel_read() instead of memcpy()
Commit df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext
data") added a bounce buffer to avoid hardened usercopy checks. Copying
to the bounce buffer was implemented with a simple memcpy() assuming
that it is always valid to read from kernel memory iff the
kern_addr_valid() check passed.
A simple, but pointless, test case like "dd if=/proc/kcore of=/dev/null"
now can easily crash the kernel, since the former execption handling on
invalid kernel addresses now doesn't work anymore.
Also adding a kern_addr_valid() implementation wouldn't help here. Most
architectures simply return 1 here, while a couple implemented a page
table walk to figure out if something is mapped at the address in
question.
With DEBUG_PAGEALLOC active mappings are established and removed all the
time, so that relying on the result of kern_addr_valid() before
executing the memcpy() also doesn't work.
Therefore simply use probe_kernel_read() to copy to the bounce buffer.
This also allows to simplify read_kcore().
At least on s390 this fixes the observed crashes and doesn't introduce
warnings that were removed with df04abfd181a ("fs/proc/kcore.c: Add
bounce buffer for ktext data"), even though the generic
probe_kernel_read() implementation uses uaccess functions.
While looking into this I'm also wondering if kern_addr_valid() could be
completely removed...(?)
Link: http://lkml.kernel.org/r/20171202132739.99971-1-heiko.carstens@de.ibm.com
Fixes: df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext data")
Fixes: f5509cc18daa ("mm: Hardened usercopy")
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r-- | fs/proc/kcore.c | 18 |
1 files changed, 5 insertions, 13 deletions
diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c index 4bc85cb8be6a..e8a93bc8285d 100644 --- a/fs/proc/kcore.c +++ b/fs/proc/kcore.c @@ -512,23 +512,15 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) return -EFAULT; } else { if (kern_addr_valid(start)) { - unsigned long n; - /* * Using bounce buffer to bypass the * hardened user copy kernel text checks. */ - memcpy(buf, (char *) start, tsz); - n = copy_to_user(buffer, buf, tsz); - /* - * We cannot distinguish between fault on source - * and fault on destination. When this happens - * we clear too and hope it will trigger the - * EFAULT again. - */ - if (n) { - if (clear_user(buffer + tsz - n, - n)) + if (probe_kernel_read(buf, (void *) start, tsz)) { + if (clear_user(buffer, tsz)) + return -EFAULT; + } else { + if (copy_to_user(buffer, buf, tsz)) return -EFAULT; } } else { |