proc: fix the issue of proc_mem_open returning NULL

[ 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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/proc/base.c b/fs/proc/base.c
index a2541f5204af066c57bbace26b57361b88b8a468..d060af34a6e837cd6f43493fe19389929b1e4064 100644 (file)
--- 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 8f5ad591d76256a92ac3719227e4270931e2a9a0..08a06fd37f0e11c91162adf3ddacb7ee46d0e5d9 100644 (file)
--- 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 bce6745330003174ed2161e31978377477cfbd70..59bfd61d653aaead0d06ce601b3685c1c6c12992 100644 (file)
--- 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;