Messages in this thread | | | Date | Thu, 28 Apr 2016 21:20:10 +0200 | From | Mateusz Guzik <> | Subject | Re: [PATCH] proc: prevent accessing /proc/<PID>/environ until it's ready |
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On Thu, Apr 28, 2016 at 09:04:18PM +0200, Mathias Krause wrote: > 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. > > Reported-at: https://forums.grsecurity.net/viewtopic.php?f=3&t=4363 > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=116461 > --- > fs/proc/base.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index 4f764c2ac1a5..45f2162e55b2 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -955,7 +955,8 @@ static ssize_t environ_read(struct file *file, char __user *buf, > struct mm_struct *mm = file->private_data; > unsigned long env_start, env_end; > > - if (!mm) > + /* Ensure the process spawned far enough to have an environment. */ > + if (!mm || !mm->env_end) > return 0; > > page = (char *)__get_free_page(GFP_TEMPORARY);
In this case get_cmdline in mm/util.c should also be patched for completness. It tests for arg_end, but later accesses env_end.
-- Mateusz Guzik
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