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| author | Mathias Krause <minipli@googlemail.com> | 2016-05-05 16:22:26 -0700 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2016-06-15 21:28:14 +0100 |
| commit | 99cfe931aa948c3af2f288f9d603bddbbc456a90 (patch) | |
| tree | 3ba984846f6bb55377233a6a00195cef8d8b6a88 | |
| parent | 05c5678247404392ef9b0e57b1f1250a50db0aa7 (diff) | |
| download | lwn-99cfe931aa948c3af2f288f9d603bddbbc456a90.tar.gz lwn-99cfe931aa948c3af2f288f9d603bddbbc456a90.zip | |
proc: prevent accessing /proc/<PID>/environ until it's ready
commit 8148a73c9901a8794a50f950083c00ccf97d43b3 upstream.
If /proc/<PID>/environ gets read before the envp[] array is fully set up
in create_{aout,elf,elf_fdpic,flat}_tables(), we might end up trying to
read more bytes than are actually written, as env_start will already be
set but env_end will still be zero, making the range calculation
underflow, allowing to read beyond the end of what has been written.
Fix this as it is done for /proc/<PID>/cmdline by testing env_end for
zero. It is, apparently, intentionally set last in create_*_tables().
This bug was found by the PaX size_overflow plugin that detected the
arithmetic underflow of 'this_len = env_end - (env_start + src)' when
env_end is still zero.
The expected consequence is that userland trying to access
/proc/<PID>/environ of a not yet fully set up process may get
inconsistent data as we're in the middle of copying in the environment
variables.
Fixes: https://forums.grsecurity.net/viewtopic.php?f=3&t=4363
Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=116461
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Emese Revfy <re.emese@gmail.com>
Cc: Pax Team <pageexec@freemail.hu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Mateusz Guzik <mguzik@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
| -rw-r--r-- | fs/proc/base.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/fs/proc/base.c b/fs/proc/base.c index 1ace83d004be..402976ab746a 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -905,7 +905,8 @@ static ssize_t environ_read(struct file *file, char __user *buf, mm = mm_for_maps(task); ret = PTR_ERR(mm); - if (!mm || IS_ERR(mm)) + /* Ensure the process spawned far enough to have an environment. */ + if (!mm || IS_ERR(mm) || !mm->env_end) goto out_free; ret = 0; |