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proc: Track /proc/$pid/attr/ opener mm_struct 

Commit bfb819ea20 ("proc: Check /proc/$pid/attr/ writes against file opener")
tried to make sure that there could not be a confusion between the opener of
a /proc/$pid/attr/ file and the writer. It used struct cred to make sure
the privileges didn't change. However, there were existing cases where a more
privileged thread was passing the opened fd to a differently privileged thread
(during container setup). Instead, use mm_struct to track whether the opener
and writer are still the same process. (This is what several other proc files
already do, though for different reasons.)

Reported-by: Christian Brauner <christian.brauner@ubuntu.com>
Reported-by: Andrea Righi <andrea.righi@canonical.com>
Tested-by: Andrea Righi <andrea.righi@canonical.com>
Fixes: bfb819ea20 ("proc: Check /proc/$pid/attr/ writes against file opener")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kees Cook 2021-06-08 10:12:21 -07:00 committed by Linus Torvalds
parent 4c8684fe55
commit 591a22c14d
1 changed files with 8 additions and 1 deletions
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9
fs/proc/base.c
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@ -2674,6 +2674,11 @@ static int proc_pident_readdir(struct file *file, struct dir_context *ctx,
}
#ifdef CONFIG_SECURITY
static int proc_pid_attr_open(struct inode *inode, struct file *file)
{
return __mem_open(inode, file, PTRACE_MODE_READ_FSCREDS);
}
static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,
size_t count, loff_t *ppos)
{
@ -2704,7 +2709,7 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
int rv;
/* A task may only write when it was the opener. */
if (file->f_cred != current_real_cred())
if (file->private_data != current->mm)
return -EPERM;
rcu_read_lock();
@ -2754,9 +2759,11 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
}
static const struct file_operations proc_pid_attr_operations = {
.open = proc_pid_attr_open,
.read = proc_pid_attr_read,
.write = proc_pid_attr_write,
.llseek = generic_file_llseek,
.release = mem_release,
};
#define LSM_DIR_OPS(LSM) \