path: root/fs
diff options
authorCalvin Owens <calvinowens@fb.com>2015-09-09 15:35:54 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-09-10 13:29:01 -0700
commitbdb4d100afe9818aebd1d98ced575c5ef143456c (patch)
tree154a6d4360aac40ccb8ea815e464b4a3f9d6aab4 /fs
parentd3691d2c6d3e72624c987bbef6f322631bbb2d5d (diff)
procfs: always expose /proc/<pid>/map_files/ and make it readable
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and is only exposed if CONFIG_CHECKPOINT_RESTORE is set. Each mapped file region gets a symlink in /proc/<pid>/map_files/ corresponding to the virtual address range at which it is mapped. The symlinks work like the symlinks in /proc/<pid>/fd/, so you can follow them to the backing file even if that backing file has been unlinked. Currently, files which are mapped, unlinked, and closed are impossible to stat() from userspace. Exposing /proc/<pid>/map_files/ closes this functionality "hole". Not being able to stat() such files makes noticing and explicitly accounting for the space they use on the filesystem impossible. You can work around this by summing up the space used by every file in the filesystem and subtracting that total from what statfs() tells you, but that obviously isn't great, and it becomes unworkable once your filesystem becomes large enough. This patch moves map_files/ out from behind CONFIG_CHECKPOINT_RESTORE, and adjusts the permissions enforced on it as follows: * proc_map_files_lookup() * proc_map_files_readdir() * map_files_d_revalidate() Remove the CAP_SYS_ADMIN restriction, leaving only the current restriction requiring PTRACE_MODE_READ. The information made available to userspace by these three functions is already available in /proc/PID/maps with MODE_READ, so I don't see any reason to limit them any further (see below for more detail). * proc_map_files_follow_link() This stub has been added, and requires that the user have CAP_SYS_ADMIN in order to follow the links in map_files/, since there was concern on LKML both about the potential for bypassing permissions on ancestor directories in the path to files pointed to, and about what happens with more exotic memory mappings created by some drivers (ie dma-buf). In older versions of this patch, I changed every permission check in the four functions above to enforce MODE_ATTACH instead of MODE_READ. This was an oversight on my part, and after revisiting the discussion it seems that nobody was concerned about anything outside of what is made possible by ->follow_link(). So in this version, I've left the checks for PTRACE_MODE_READ as-is. [akpm@linux-foundation.org: catch up with concurrent proc_pid_follow_link() changes] Signed-off-by: Calvin Owens <calvinowens@fb.com> Reviewed-by: Kees Cook <keescook@chromium.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Cyrill Gorcunov <gorcunov@openvz.org> Cc: Joe Perches <joe@perches.com> Cc: Kirill A. Shutemov <kirill@shutemov.name> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
1 files changed, 24 insertions, 19 deletions
diff --git a/fs/proc/base.c b/fs/proc/base.c
index aa50d1ac28fc..60c71b10eaee 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1836,8 +1836,6 @@ end_instantiate:
return dir_emit(ctx, name, len, 1, DT_UNKNOWN);
* dname_to_vma_addr - maps a dentry name into two unsigned longs
* which represent vma start and end addresses.
@@ -1864,11 +1862,6 @@ static int map_files_d_revalidate(struct dentry *dentry, unsigned int flags)
if (flags & LOOKUP_RCU)
return -ECHILD;
- if (!capable(CAP_SYS_ADMIN)) {
- status = -EPERM;
- goto out_notask;
- }
inode = d_inode(dentry);
task = get_proc_task(inode);
if (!task)
@@ -1957,6 +1950,29 @@ struct map_files_info {
unsigned char name[4*sizeof(long)+2]; /* max: %lx-%lx\0 */
+ * Only allow CAP_SYS_ADMIN to follow the links, due to concerns about how the
+ * symlinks may be used to bypass permissions on ancestor directories in the
+ * path to the file in question.
+ */
+static const char *
+proc_map_files_follow_link(struct dentry *dentry, void **cookie)
+ if (!capable(CAP_SYS_ADMIN))
+ return ERR_PTR(-EPERM);
+ return proc_pid_follow_link(dentry, NULL);
+ * Identical to proc_pid_link_inode_operations except for follow_link()
+ */
+static const struct inode_operations proc_map_files_link_inode_operations = {
+ .readlink = proc_pid_readlink,
+ .follow_link = proc_map_files_follow_link,
+ .setattr = proc_setattr,
static int
proc_map_files_instantiate(struct inode *dir, struct dentry *dentry,
struct task_struct *task, const void *ptr)
@@ -1972,7 +1988,7 @@ proc_map_files_instantiate(struct inode *dir, struct dentry *dentry,
ei = PROC_I(inode);
ei->op.proc_get_link = proc_map_files_get_link;
- inode->i_op = &proc_pid_link_inode_operations;
+ inode->i_op = &proc_map_files_link_inode_operations;
inode->i_size = 64;
inode->i_mode = S_IFLNK;
@@ -1996,10 +2012,6 @@ static struct dentry *proc_map_files_lookup(struct inode *dir,
int result;
struct mm_struct *mm;
- result = -EPERM;
- if (!capable(CAP_SYS_ADMIN))
- goto out;
result = -ENOENT;
task = get_proc_task(dir);
if (!task)
@@ -2053,10 +2065,6 @@ proc_map_files_readdir(struct file *file, struct dir_context *ctx)
struct map_files_info *p;
int ret;
- ret = -EPERM;
- if (!capable(CAP_SYS_ADMIN))
- goto out;
ret = -ENOENT;
task = get_proc_task(file_inode(file));
if (!task)
@@ -2245,7 +2253,6 @@ static const struct file_operations proc_timers_operations = {
.llseek = seq_lseek,
.release = seq_release_private,
static int proc_pident_instantiate(struct inode *dir,
struct dentry *dentry, struct task_struct *task, const void *ptr)
@@ -2744,9 +2751,7 @@ static const struct inode_operations proc_task_inode_operations;
static const struct pid_entry tgid_base_stuff[] = {
DIR("task", S_IRUGO|S_IXUGO, proc_task_inode_operations, proc_task_operations),
DIR("fd", S_IRUSR|S_IXUSR, proc_fd_inode_operations, proc_fd_operations),
DIR("map_files", S_IRUSR|S_IXUSR, proc_map_files_inode_operations, proc_map_files_operations),
DIR("fdinfo", S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, proc_fdinfo_operations),
DIR("ns", S_IRUSR|S_IXUGO, proc_ns_dir_inode_operations, proc_ns_dir_operations),

Privacy Policy