uprobes: Fix prepare_uprobe() race with itself

install_breakpoint() is called under mm->mmap_sem, this protects
set_swbp() but not prepare_uprobe(). Two or more different tasks
can call install_breakpoint()->prepare_uprobe() at the same time,
this leads to numerous problems if UPROBE_COPY_INSN is not set.

Just for example, the second copy_insn() can corrupt the already
analyzed/fixuped uprobe->arch.insn and race with handle_swbp().

This patch simply adds uprobe->copy_mutex to serialize this code.
We could probably reuse ->consumer_rwsem, but this would mean that
consumer->handler() can not use mm->mmap_sem, not good.

Note: this is another temporary ugly hack until we move this logic
into uprobe_register().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 4f315fa94c52..7f62b30c4172 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -89,6 +89,7 @@ struct uprobe {
         struct rb_node          rb_node;        /* node in the rb tree */
         atomic_t                ref;
         struct rw_semaphore     consumer_rwsem;
+        struct mutex            copy_mutex;     /* TODO: kill me and UPROBE_COPY_INSN */
         struct list_head        pending_list;
         struct uprobe_consumer  *consumers;
         struct inode            *inode;         /* Also hold a ref to inode */
@@ -444,6 +445,7 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
         uprobe->inode = igrab(inode);
         uprobe->offset = offset;
         init_rwsem(&uprobe->consumer_rwsem);
+        mutex_init(&uprobe->copy_mutex);
 
         /* add to uprobes_tree, sorted on inode:offset */
         cur_uprobe = insert_uprobe(uprobe);
@@ -578,6 +580,10 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
         if (uprobe->flags & UPROBE_COPY_INSN)
                 return ret;
 
+        mutex_lock(&uprobe->copy_mutex);
+        if (uprobe->flags & UPROBE_COPY_INSN)
+                goto out;
+
         ret = copy_insn(uprobe, file);
         if (ret)
                 goto out;
@@ -598,6 +604,8 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
         uprobe->flags |= UPROBE_COPY_INSN;
 
  out:
+        mutex_unlock(&uprobe->copy_mutex);
+
         return ret;
 }