lkml.org 
[lkml]   [2018]   [Sep]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] proc/kcore: fix invalid memory access in multi-page read optimization
On Wed, Aug 29, 2018 at 06:04:07AM +0200, Dominique Martinet wrote:
> The 'm' kcore_list item can point to kclist_head, and it is incorrect to
> look at m->addr / m->size in this case.
> There is no choice but to run through the list of entries for every address
> if we did not find any entry in the previous iteration
>
> Fixes: bf991c2231117 ("proc/kcore: optimize multiple page reads")
> Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
> ---
>
> I guess now I'm looking at bf991c2231117 again that it would be slightly
> more efficient to remove the !m check and initialize m to point to
> kclist_head like this:
> m = list_entry(&kclist_head, struct kcore_list, list);
> but it feels a bit forced to me; deferring the choice to others.

Good catch! Sorry I missed this last week, Google decided this was spam
for some reason. How about fixing it like this? One less conditional in
the common case, no hacky list_entry :)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index ad72261ee3fe..578926032880 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -464,6 +464,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
ret = -EFAULT;
goto out;
}
+ m = NULL;
} else if (m->type == KCORE_VMALLOC) {
vread(buf, (char *)start, tsz);
/* we have to zero-fill user buffer even if no read */
> fs/proc/kcore.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index ad72261ee3fe..50036f6e1f52 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -451,7 +451,8 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> * If this is the first iteration or the address is not within
> * the previous entry, search for a matching entry.
> */
> - if (!m || start < m->addr || start >= m->addr + m->size) {
> + if (!m || &m->list == &kclist_head || start < m->addr ||
> + start >= m->addr + m->size) {
> list_for_each_entry(m, &kclist_head, list) {
> if (start >= m->addr &&
> start < m->addr + m->size)
> --
> 2.17.1
>

\
 
 \ /
  Last update: 2018-09-04 20:04    [W:0.063 / U:8.564 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site