From 578d7699e5c2add8c2e9549d9d75dfb56c460cb3 Mon Sep 17 00:00:00 2001 From: Ben Wolsieffer Date: Thu, 14 Sep 2023 12:30:20 -0400 Subject: proc: nommu: /proc//maps: release mmap read lock The no-MMU implementation of /proc//map doesn't normally release the mmap read lock, because it uses !IS_ERR_OR_NULL(_vml) to determine whether to release the lock. Since _vml is NULL when the end of the mappings is reached, the lock is not released. Reading /proc/1/maps twice doesn't cause a hang because it only takes the read lock, which can be taken multiple times and therefore doesn't show any problem if the lock isn't released. Instead, you need to perform some operation that attempts to take the write lock after reading /proc//maps. To actually reproduce the bug, compile the following code as 'proc_maps_bug': #include #include #include int main(int argc, char *argv[]) { void *buf; sleep(1); buf = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); puts("mmap returned"); return 0; } Then, run: ./proc_maps_bug &; cat /proc/$!/maps; fg Without this patch, mmap() will hang and the command will never complete. This code was incorrectly adapted from the MMU implementation, which at the time released the lock in m_next() before returning the last entry. The MMU implementation has diverged further from the no-MMU version since then, so this patch brings their locking and error handling into sync, fixing the bug and hopefully avoiding similar issues in the future. Link: https://lkml.kernel.org/r/20230914163019.4050530-2-ben.wolsieffer@hefring.com Fixes: 47fecca15c09 ("fs/proc/task_nommu.c: don't use priv->task->mm") Signed-off-by: Ben Wolsieffer Acked-by: Oleg Nesterov Cc: Giulio Benetti Cc: Greg Ungerer Cc: Signed-off-by: Andrew Morton --- fs/proc/task_nommu.c | 27 +++++++++++++++------------ 1 file changed, 15 insertions(+), 12 deletions(-) (limited to 'fs') diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c index a8ac0dd8041e..bc2e843f4810 100644 --- a/fs/proc/task_nommu.c +++ b/fs/proc/task_nommu.c @@ -192,11 +192,16 @@ static void *m_start(struct seq_file *m, loff_t *pos) return ERR_PTR(-ESRCH); mm = priv->mm; - if (!mm || !mmget_not_zero(mm)) + if (!mm || !mmget_not_zero(mm)) { + put_task_struct(priv->task); + priv->task = NULL; return NULL; + } if (mmap_read_lock_killable(mm)) { mmput(mm); + put_task_struct(priv->task); + priv->task = NULL; return ERR_PTR(-EINTR); } @@ -205,23 +210,21 @@ static void *m_start(struct seq_file *m, loff_t *pos) if (vma) return vma; - mmap_read_unlock(mm); - mmput(mm); return NULL; } -static void m_stop(struct seq_file *m, void *_vml) +static void m_stop(struct seq_file *m, void *v) { struct proc_maps_private *priv = m->private; + struct mm_struct *mm = priv->mm; - if (!IS_ERR_OR_NULL(_vml)) { - mmap_read_unlock(priv->mm); - mmput(priv->mm); - } - if (priv->task) { - put_task_struct(priv->task); - priv->task = NULL; - } + if (!priv->task) + return; + + mmap_read_unlock(mm); + mmput(mm); + put_task_struct(priv->task); + priv->task = NULL; } static void *m_next(struct seq_file *m, void *_p, loff_t *pos) -- cgit v1.2.3-58-ga151 From fe4419801617514765974f3e796269bc512ad146 Mon Sep 17 00:00:00 2001 From: Ben Wolsieffer Date: Fri, 15 Sep 2023 12:00:56 -0400 Subject: proc: nommu: fix empty /proc//maps On no-MMU, /proc//maps reads as an empty file. This happens because find_vma(mm, 0) always returns NULL (assuming no vma actually contains the zero address, which is normally the case). To fix this bug and improve the maintainability in the future, this patch makes the no-MMU implementation as similar as possible to the MMU implementation. The only remaining differences are the lack of hold/release_task_mempolicy and the extra code to shoehorn the gate vma into the iterator. This has been tested on top of 6.5.3 on an STM32F746. Link: https://lkml.kernel.org/r/20230915160055.971059-2-ben.wolsieffer@hefring.com Fixes: 0c563f148043 ("proc: remove VMA rbtree use from nommu") Signed-off-by: Ben Wolsieffer Cc: Davidlohr Bueso Cc: Giulio Benetti Cc: Liam R. Howlett Cc: Matthew Wilcox (Oracle) Cc: Oleg Nesterov Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- fs/proc/internal.h | 2 -- fs/proc/task_nommu.c | 37 ++++++++++++++++++++++--------------- 2 files changed, 22 insertions(+), 17 deletions(-) (limited to 'fs') diff --git a/fs/proc/internal.h b/fs/proc/internal.h index 9dda7e54b2d0..9a8f32f21ff5 100644 --- a/fs/proc/internal.h +++ b/fs/proc/internal.h @@ -289,9 +289,7 @@ struct proc_maps_private { struct inode *inode; struct task_struct *task; struct mm_struct *mm; -#ifdef CONFIG_MMU struct vma_iterator iter; -#endif #ifdef CONFIG_NUMA struct mempolicy *task_mempolicy; #endif diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c index bc2e843f4810..7cebd397cc26 100644 --- a/fs/proc/task_nommu.c +++ b/fs/proc/task_nommu.c @@ -175,15 +175,28 @@ static int show_map(struct seq_file *m, void *_p) return nommu_vma_show(m, _p); } -static void *m_start(struct seq_file *m, loff_t *pos) +static struct vm_area_struct *proc_get_vma(struct proc_maps_private *priv, + loff_t *ppos) +{ + struct vm_area_struct *vma = vma_next(&priv->iter); + + if (vma) { + *ppos = vma->vm_start; + } else { + *ppos = -1UL; + } + + return vma; +} + +static void *m_start(struct seq_file *m, loff_t *ppos) { struct proc_maps_private *priv = m->private; + unsigned long last_addr = *ppos; struct mm_struct *mm; - struct vm_area_struct *vma; - unsigned long addr = *pos; - /* See m_next(). Zero at the start or after lseek. */ - if (addr == -1UL) + /* See proc_get_vma(). Zero at the start or after lseek. */ + if (last_addr == -1UL) return NULL; /* pin the task and mm whilst we play with them */ @@ -205,12 +218,9 @@ static void *m_start(struct seq_file *m, loff_t *pos) return ERR_PTR(-EINTR); } - /* start the next element from addr */ - vma = find_vma(mm, addr); - if (vma) - return vma; + vma_iter_init(&priv->iter, mm, last_addr); - return NULL; + return proc_get_vma(priv, ppos); } static void m_stop(struct seq_file *m, void *v) @@ -227,12 +237,9 @@ static void m_stop(struct seq_file *m, void *v) priv->task = NULL; } -static void *m_next(struct seq_file *m, void *_p, loff_t *pos) +static void *m_next(struct seq_file *m, void *_p, loff_t *ppos) { - struct vm_area_struct *vma = _p; - - *pos = vma->vm_end; - return find_vma(vma->vm_mm, vma->vm_end); + return proc_get_vma(m->private, ppos); } static const struct seq_operations proc_pid_maps_ops = { -- cgit v1.2.3-58-ga151