Sorry for double-posting, but it seems that this patch didn't reach
lkml. Let me resend it just on case. Plus another patch in reply, on
top of this change.
-------------------------------------------------------------------------------
Subject: [PATCH] uprobes: Shift ->readpage check from __copy_insn() to
uprobe_register()
copy_insn() fails with -EIO if ->readpage == NULL, but this error
is not propagated unless uprobe_register() path finds ->mm which
already mmaps this file. In this case (say) "perf record" does not
actually install the probe, but the user can't know about this.
Move this check into uprobe_register() so that this problem can be
detected earlier and reported to user.
Note: this is still not perfect,
- copy_insn() and arch_uprobe_analyze_insn() should be called
by uprobe_register() but this is not simple, we need vm_file
for read_mapping_page() (although perhaps we can pass NULL),
and we need ->mm for is_64bit_mm() (although this logic is
broken anyway).
- uprobe_register() should be called by create_trace_uprobe(),
not by probe_event_enable(), so that an error can be detected
at "perf probe -x" time. This also needs more changes in the
core uprobe code, uprobe register/unregister interface was
poorly designed from the very beginning.
Reported-by: Denys Vlasenko <dvlas...@redhat.com>
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
kernel/events/uprobes.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 3b02c72..c56b13e 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -536,9 +536,6 @@ static int __copy_insn(struct address_space *mapping,
struct file *filp,
void *insn, int nbytes, loff_t offset)
{
struct page *page;
-
- if (!mapping->a_ops->readpage)
- return -EIO;
/*
* Ensure that the page that has the original instruction is
* populated and in page-cache.
@@ -879,6 +876,9 @@ int uprobe_register(struct inode *inode, loff_t offset,
struct uprobe_consumer *
if (!uc->handler && !uc->ret_handler)
return -EINVAL;
+ /* copy_insn()->read_mapping_page() needs ->readpage() */
+ if (!inode->i_mapping->a_ops->readpage)
+ return -EIO;
/* Racy, just to catch the obvious mistakes */
if (offset > i_size_read(inode))
return -EINVAL;
--
1.5.5.1
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