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tracefs: Only clobber mode/uid/gid on remount if asked

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Users may have explicitly configured their tracefs permissions; we
shouldn't overwrite those just because a second mount appeared.

Only clobber if the options were provided at mount time.

Note: the previous behavior was especially surprising in the presence of
automounted /sys/kernel/debug/tracing/.

Existing behavior:

  ## Pre-existing status: tracefs is 0755.
  # stat -c '%A' /sys/kernel/tracing/
  drwxr-xr-x

  ## (Re)trigger the automount.
  # umount /sys/kernel/debug/tracing
  # stat -c '%A' /sys/kernel/debug/tracing/.
  drwx------

  ## Unexpected: the automount changed mode for other mount instances.
  # stat -c '%A' /sys/kernel/tracing/
  drwx------

New behavior (after this change):

  ## Pre-existing status: tracefs is 0755.
  # stat -c '%A' /sys/kernel/tracing/
  drwxr-xr-x

  ## (Re)trigger the automount.
  # umount /sys/kernel/debug/tracing
  # stat -c '%A' /sys/kernel/debug/tracing/.
  drwxr-xr-x

  ## Expected: the automount does not change other mount instances.
  # stat -c '%A' /sys/kernel/tracing/
  drwxr-xr-x

Link: https://lkml.kernel.org/r/20220826174353.2.Iab6e5ea57963d6deca5311b27fb7226790d44406@changeid

Cc: stable@vger.kernel.org
Fixes: 4282d60689 ("tracefs: Add new tracefs file system")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Brian Norris 2022-08-26 17:44:17 -07:00 committed by Steven Rostedt (Google)
parent 1efda38d6f
commit 47311db8e8
1 changed files with 23 additions and 8 deletions
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31
fs/tracefs/inode.c
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@ -141,6 +141,8 @@ struct tracefs_mount_opts {
kuid_t uid;
kgid_t gid;
umode_t mode;
/* Opt_* bitfield. */
unsigned int opts;
};
enum {
@ -241,6 +243,7 @@ static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
kgid_t gid;
char *p;
opts->opts = 0;
opts->mode = TRACEFS_DEFAULT_MODE;
while ((p = strsep(&data, ",")) != NULL) {
@ -275,24 +278,36 @@ static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
* but traditionally tracefs has ignored all mount options
*/
}
opts->opts |= BIT(token);
}
return 0;
}
static int tracefs_apply_options(struct super_block *sb)
static int tracefs_apply_options(struct super_block *sb, bool remount)
{
struct tracefs_fs_info *fsi = sb->s_fs_info;
struct inode *inode = d_inode(sb->s_root);
struct tracefs_mount_opts *opts = &fsi->mount_opts;
inode->i_mode &= ~S_IALLUGO;
inode->i_mode |= opts->mode;
/*
* On remount, only reset mode/uid/gid if they were provided as mount
* options.
*/
inode->i_uid = opts->uid;
if (!remount || opts->opts & BIT(Opt_mode)) {
inode->i_mode &= ~S_IALLUGO;
inode->i_mode |= opts->mode;
}
/* Set all the group ids to the mount option */
set_gid(sb->s_root, opts->gid);
if (!remount || opts->opts & BIT(Opt_uid))
inode->i_uid = opts->uid;
if (!remount || opts->opts & BIT(Opt_gid)) {
/* Set all the group ids to the mount option */
set_gid(sb->s_root, opts->gid);
}
return 0;
}
@ -307,7 +322,7 @@ static int tracefs_remount(struct super_block *sb, int *flags, char *data)
if (err)
goto fail;
tracefs_apply_options(sb);
tracefs_apply_options(sb, true);
fail:
return err;
@ -359,7 +374,7 @@ static int trace_fill_super(struct super_block *sb, void *data, int silent)
sb->s_op = &tracefs_super_operations;
tracefs_apply_options(sb);
tracefs_apply_options(sb, false);
return 0;