From: Penglei Jiang superman.xpt@gmail.com

[ Upstream commit 65c66047259fad1b868d4454bc5af95b46a5f954 ]

proc_mem_open() can return an errno, NULL, or mm_struct*. If it fails to acquire mm, it returns NULL, but the caller does not check for the case when the return value is NULL.

The following conditions lead to failure in acquiring mm:

- The task is a kernel thread (PF_KTHREAD) - The task is exiting (PF_EXITING)

Changes:

- Add documentation comments for the return value of proc_mem_open(). - Add checks in the caller to return -ESRCH when proc_mem_open() returns NULL.

Link: https://lkml.kernel.org/r/20250404063357.78891-1-superman.xpt@gmail.com Reported-by: syzbot+f9238a0a31f9b5603fef@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/000000000000f52642060d4e3750@google.com Signed-off-by: Penglei Jiang superman.xpt@gmail.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Adrian Ratiu adrian.ratiu@collabora.com Cc: Christian Brauner brauner@kernel.org Cc: Felix Moessbauer felix.moessbauer@siemens.com Cc: Jeff layton jlayton@kernel.org Cc: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Mateusz Guzik mjguzik@gmail.com Cc: Thomas Gleinxer tglx@linutronix.de Cc: xu xin xu.xin16@zte.com.cn Cc: Alexey Dobriyan adobriyan@gmail.com Signed-off-by: Andrew Morton akpm@linux-foundation.org [ acsjakub: applied cleanly ] Signed-off-by: Jakub Acs acsjakub@amazon.de --- fs/proc/base.c | 12 +++++++++--- fs/proc/task_mmu.c | 12 ++++++------ fs/proc/task_nommu.c | 4 ++-- 3 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c index a2541f5204af..d060af34a6e8 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -828,7 +828,13 @@ static const struct file_operations proc_single_file_operations = { .release = single_release, };

- +/* + * proc_mem_open() can return errno, NULL or mm_struct*. + * + * - Returns NULL if the task has no mm (PF_KTHREAD or PF_EXITING) + * - Returns mm_struct* on success + * - Returns error code on failure + */ struct mm_struct *proc_mem_open(struct inode *inode, unsigned int mode) { struct task_struct *task = get_proc_task(inode); @@ -853,8 +859,8 @@ static int __mem_open(struct inode *inode, struct file *file, unsigned int mode) { struct mm_struct *mm = proc_mem_open(inode, mode);

- if (IS_ERR(mm)) - return PTR_ERR(mm); + if (IS_ERR_OR_NULL(mm)) + return mm ? PTR_ERR(mm) : -ESRCH;

file->private_data = mm; return 0; diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 8f5ad591d762..08a06fd37f0e 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -212,8 +212,8 @@ static int proc_maps_open(struct inode *inode, struct file *file,

priv->inode = inode; priv->mm = proc_mem_open(inode, PTRACE_MODE_READ); - if (IS_ERR(priv->mm)) { - int err = PTR_ERR(priv->mm); + if (IS_ERR_OR_NULL(priv->mm)) { + int err = priv->mm ? PTR_ERR(priv->mm) : -ESRCH;

seq_release_private(inode, file); return err; @@ -1316,8 +1316,8 @@ static int smaps_rollup_open(struct inode *inode, struct file *file)

priv->inode = inode; priv->mm = proc_mem_open(inode, PTRACE_MODE_READ); - if (IS_ERR(priv->mm)) { - ret = PTR_ERR(priv->mm); + if (IS_ERR_OR_NULL(priv->mm)) { + ret = priv->mm ? PTR_ERR(priv->mm) : -ESRCH;

single_release(inode, file); goto out_free; @@ -2049,8 +2049,8 @@ static int pagemap_open(struct inode *inode, struct file *file) struct mm_struct *mm;

mm = proc_mem_open(inode, PTRACE_MODE_READ); - if (IS_ERR(mm)) - return PTR_ERR(mm); + if (IS_ERR_OR_NULL(mm)) + return mm ? PTR_ERR(mm) : -ESRCH; file->private_data = mm; return 0; } diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c index bce674533000..59bfd61d653a 100644 --- a/fs/proc/task_nommu.c +++ b/fs/proc/task_nommu.c @@ -260,8 +260,8 @@ static int maps_open(struct inode *inode, struct file *file,

priv->inode = inode; priv->mm = proc_mem_open(inode, PTRACE_MODE_READ); - if (IS_ERR(priv->mm)) { - int err = PTR_ERR(priv->mm); + if (IS_ERR_OR_NULL(priv->mm)) { + int err = priv->mm ? PTR_ERR(priv->mm) : -ESRCH;

seq_release_private(inode, file); return err;