* [PATCH 1/3] Btrfs-progs: fix mount point detection due to partial prefix match
@ 2019-01-14 13:30 fdmanana
2019-01-14 13:59 ` David Disseldorp
0 siblings, 1 reply; 3+ messages in thread
From: fdmanana @ 2019-01-14 13:30 UTC (permalink / raw)
To: linux-btrfs; +Cc: ddis, Filipe Manana
From: Filipe Manana <fdmanana@suse.com>
When attempting to find the mount point of a path we can end up returning
an incorrect mount point. This happens because we consider a mount point
valid for the given path even if it matches only partially the patch.
Consider the following example, which makes btrfs receive fail:
$ truncate -s 1G disk1
$ truncate -s 1G disk2
$ losetup /dev/loop1 disk1
$ losetup /dev/loop2 disk2
$ mkfs.btrfs -f /dev/loop1
$ mkfs.btrfs -f /dev/loop2
$ mount /dev/loop1 /mnt
$ mkdir /mnt/ddis
$ mkdir /mnt/ddis-not-a-mount
$ mount /dev/loop2 /mnt/ddis
$ echo "some data" > /mnt/ddis/file
$ btrfs subvolume snapshot -r /mnt/ddis /mnt/ddis/snap
$ btrfs send -f /tmp/send.data /mnt/ddis/snap
$ btrfs receive -f /tmp/send.data /mnt/ddis-not-a-mount
At subvol snap
ERROR: chown failed: No such file or directory
In that example btrfs receive passes the path "/mnt/ddis-not-a-mount" to
find_mount_root() which picks "/mnt/ddis" as the mount point instead of
"/mnt". The wrong decision happens because "/mnt/ddis" is the longest
string found that is a prefix of "/mnt/ddis-not-a-mount", however it
shouldn't be considered valid because what follows the substring "ddis"
in the given path is not a path separator ("/") nor the null character
('\0'). So fix find_mount_root() to check for the presence of a path
separator or a null byte character after if finds a mount point string
that matches the given path.
A test case will follow soon in a separate patch.
Reported-by: David Disseldorp <ddis@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
utils.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/utils.c b/utils.c
index 3a4bc92a..6616630b 100644
--- a/utils.c
+++ b/utils.c
@@ -2064,7 +2064,8 @@ int find_mount_root(const char *path, char **mount_root)
while ((ent = getmntent(mnttab))) {
len = strlen(ent->mnt_dir);
- if (strncmp(ent->mnt_dir, path, len) == 0) {
+ if (strncmp(ent->mnt_dir, path, len) == 0 &&
+ (path[len] == '/' || path[len] == '\0')) {
/* match found and use the latest match */
if (longest_matchlen <= len) {
free(longest_match);
--
2.11.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH 1/3] Btrfs-progs: fix mount point detection due to partial prefix match
2019-01-14 13:30 [PATCH 1/3] Btrfs-progs: fix mount point detection due to partial prefix match fdmanana
@ 2019-01-14 13:59 ` David Disseldorp
2019-01-14 14:12 ` Filipe Manana
0 siblings, 1 reply; 3+ messages in thread
From: David Disseldorp @ 2019-01-14 13:59 UTC (permalink / raw)
To: fdmanana; +Cc: linux-btrfs, Filipe Manana
On Mon, 14 Jan 2019 13:30:24 +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
>
> When attempting to find the mount point of a path we can end up returning
> an incorrect mount point. This happens because we consider a mount point
> valid for the given path even if it matches only partially the patch.
s/patch/path/? "...even if it only partially matches" might be a bit
clearer.
> diff --git a/utils.c b/utils.c
> index 3a4bc92a..6616630b 100644
> --- a/utils.c
> +++ b/utils.c
> @@ -2064,7 +2064,8 @@ int find_mount_root(const char *path, char **mount_root)
>
> while ((ent = getmntent(mnttab))) {
> len = strlen(ent->mnt_dir);
> - if (strncmp(ent->mnt_dir, path, len) == 0) {
> + if (strncmp(ent->mnt_dir, path, len) == 0 &&
> + (path[len] == '/' || path[len] == '\0')) {
Looks good and works for me.
Reviewed-by: David Disseldorp <ddiss@suse.de>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH 1/3] Btrfs-progs: fix mount point detection due to partial prefix match
2019-01-14 13:59 ` David Disseldorp
@ 2019-01-14 14:12 ` Filipe Manana
0 siblings, 0 replies; 3+ messages in thread
From: Filipe Manana @ 2019-01-14 14:12 UTC (permalink / raw)
To: David Disseldorp; +Cc: linux-btrfs, Filipe Manana
On Mon, Jan 14, 2019 at 1:59 PM David Disseldorp <ddiss@suse.de> wrote:
>
> On Mon, 14 Jan 2019 13:30:24 +0000, fdmanana@kernel.org wrote:
>
> > From: Filipe Manana <fdmanana@suse.com>
> >
> > When attempting to find the mount point of a path we can end up returning
> > an incorrect mount point. This happens because we consider a mount point
> > valid for the given path even if it matches only partially the patch.
>
> s/patch/path/? "...even if it only partially matches" might be a bit
> clearer.
Agreed.
David can probably correct that (and your email address from ddis@ to
ddiss@) when he picks the patch, otherwise I can send a new version.
Thanks.
>
> > diff --git a/utils.c b/utils.c
> > index 3a4bc92a..6616630b 100644
> > --- a/utils.c
> > +++ b/utils.c
> > @@ -2064,7 +2064,8 @@ int find_mount_root(const char *path, char **mount_root)
> >
> > while ((ent = getmntent(mnttab))) {
> > len = strlen(ent->mnt_dir);
> > - if (strncmp(ent->mnt_dir, path, len) == 0) {
> > + if (strncmp(ent->mnt_dir, path, len) == 0 &&
> > + (path[len] == '/' || path[len] == '\0')) {
>
> Looks good and works for me.
> Reviewed-by: David Disseldorp <ddiss@suse.de>
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2019-01-14 14:12 UTC | newest]
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2019-01-14 13:30 [PATCH 1/3] Btrfs-progs: fix mount point detection due to partial prefix match fdmanana
2019-01-14 13:59 ` David Disseldorp
2019-01-14 14:12 ` Filipe Manana
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