bpf: kprobe_multi allows BPF_F_SLEEPABLE programs, causing sleeping-in-atomic splat

BUG Superseded Varun R Mallya 2 participants 6 messages Apr 1

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Kselftest BPF Tracing BPF selftests +2 more subsystems

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Varun R Mallya

author

2026-04-01 13:44 UTC #0 lore raw

Hi,

I found a bug in the kprobe_multi BPF link creation path where the kernel fails to reject programs with BPF_F_SLEEPABLE set.

kprobe.multi programs run in an atomic/RCU context and cannot sleep. However, bpf_link_create() with BPF_TRACE_KPROBE_MULTI does not validate whether the program being attached has BPF_F_SLEEPABLE set. This allows sleepable helpers such as bpf_copy_from_user() to be invoked from a non-sleepable context, triggering a "sleeping function called from invalid context" splat.

Reproducer:

  /* crash.bpf.c */
  SEC("kprobe.multi")
  int handle_kprobe_multi_crash(struct pt_regs *ctx)
  {
      char buf[16];
      int ret;
      ret = bpf_copy_from_user(buf, sizeof(buf), (void *)ctx->sp);
      bpf_printk("bpf_copy_from_user ret: %d\n", ret);
      return 0;
  }

/* loader: manually set BPF_F_SLEEPABLE before load, then attach via
bpf_link_create() with BPF_TRACE_KPROBE_MULTI */
bpf_program__set_flags(prog, BPF_F_SLEEPABLE);

Kernel output (bpf-next 7.0.0-rc5+):

[  483.577248] BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:
169
[  483.577364] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1787, name: sudo
[  483.577420] preempt_count: 1, expected: 0
[  483.577453] RCU nest depth: 2, expected: 0
[  483.577486] INFO: lockdep is turned off.

Attachment successful! The bug is confirmed. Check 'sudo dmesg -w' for BPF prints and warnings.
Triggering v[ 483.577569] CfsPU: 7 UID: 0 PID: 1787 Comm: sudo Tainted: G W _
rea7.0.0-rc5+ #4 PREEMPT(full)
d[ 483.577571] T.ainted: [W]=WARN..

Su[ 483.577572] Hrvardware name: Bochs Bochs, BIOS iBochs 01/01/2011v

[  483.577573] Call Trace:
[  483.577575]  e<TASK>
[  483.577578]  d!dump_stack_lvl+0x54/0x70
 [  483.577582]  If __might_resched+b0x200/0x220
p[  483.577585]  f__might_fault+0x_c2c/0x80
o[  483.577587]  p_copy_from_user+y0x23/0x80
_[  483.577591]  bpf_copy_from_user+0x27/0x50
[  483.577594]  fbpf_prog_1906cf6roa66546b5e_handlem__kprobe_multi_crash+0x33/0x4d
u[  483.577596]  skprobe_multi_linek_handler+0x15d/r re0x260
[  483.577599]  t? kprobe_multi_lurink_handler+0x99n/0x260
[  483.577602]  e? __pfx_vfs_readd +0x10/0x10
0[  483.577604]   in? ksys_read+0x7c/0x100
 [  483.577605]  dm? vfs_read+0x4/0esg, x360
t[  483.577607]  fprobe_ftrace_entry+0x3b8/0x480
[  483.577609]  h? ksys_read+0x7ce /0x100
e[  483.577610]  x? fprobe_ftrace_pentry+0x93/0x480l
o[  483.577612]  it? lock_release+0x42/0x330
 [  483.577615]  ? vfs_read+0x9/0wx360
o[  483.577616]  r? __x64_sys_rt_sigaction+0xde/0xke120
[  483.577619]  ? vfs_read+0x9/0x360
[  483.577620]  d? ksys_read+0x7c./0x100
[  483.577622]  
? do_syscall_64+0x143/0xf80
[  483.577624]  ? entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  483.577625]  ? trace_irq_disable+0x1d/0xc0
[  483.577627]  ? entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  483.577631]  </TASK>

I am sending in a patch that fixes this.

Signed-off-by Varun R Mallya <[email protected]>

Varun R Mallya

author

2026-04-01 13:49 UTC #1 lore raw

PATCH 1/1 bpf: Reject sleepable kprobe_multi programs at attach time

kprobe.multi programs run in atomic/RCU context and cannot sleep. However, bpf_kprobe_multi_link_attach() did not validate whether the program being attached had the sleepable flag set, allowing sleepable helpers such as bpf_copy_from_user() to be invoked from a non-sleepable context.

This causes a "sleeping function called from invalid context" splat:

  BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:169
  in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1787, name: sudo
  preempt_count: 1, expected: 0
  RCU nest depth: 2, expected: 0

Fix this by rejecting sleepable programs early in bpf_kprobe_multi_link_attach(), before any further processing.

Fixes 0dcac272540613d41c05e89679e4ddb978b612f1 ("bpf: Add multi kprobe link")

Signed-off-by Varun R Mallya <[email protected]>

---
 kernel/trace/bpf_trace.c | 4 ++++
 1 file changed, 4 insertions(+)

kernel/trace/bpf_trace.c +4 -0

index 0b040a417442..af7079aa0f36 100644
@@ -2752,6 +2752,10 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	if (!is_kprobe_multi(prog))
 		return -EINVAL;
 
+	/* kprobe_multi is not allowed to be sleepable. */
+	if (prog->sleepable)
+		return -EINVAL;
+
 	/* Writing to context is not allowed for kprobes. */
 	if (prog->aux->kprobe_write_ctx)
 		return -EINVAL;

Signature · 1 line

2.53.0

Kumar Kartikeya Dwivedi

maintainer

2026-04-01 14:08 UTC #2 lore raw

Re: [PATCH bpf] bpf: Reject sleepable kprobe_multi programs at attach time

Quoted 14 lines · Varun R Mallya

kprobe.multi programs run in atomic/RCU context and cannot sleep. However, bpf_kprobe_multi_link_attach() did not validate whether the program being attached had the sleepable flag set, allowing sleepable helpers such as bpf_copy_from_user() to be invoked from a non-sleepable context.
This causes a "sleeping function called from invalid context" splat:
  BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:169
  in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1787, name: sudo
  preempt_count: 1, expected: 0
  RCU nest depth: 2, expected: 0

Quoted 4 lines

Fix this by rejecting sleepable programs early in bpf_kprobe_multi_link_attach(), before any further processing.
Fixes 0dcac272540613d41c05e89679e4ddb978b612f1 ("bpf: Add multi kprobe link")

Please use the right format.

Fixes 0dcac2725406 ("bpf: Add multi kprobe link")

You can add the follow to your .gitconfig to generate the fixes tag. [alias]

    fixes = log -1 --format='Fixes: %h (\"%s\")'

Quoted 10 lines

Signed-off-by Varun R Mallya <[email protected]>
---
 kernel/trace/bpf_trace.c | 4 ++++
 1 file changed, 4 insertions(+)
kernel/trace/bpf_trace.c +0 -0
index 0b040a417442..af7079aa0f36 100644

kernel/trace/bpf_trace.c int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr · line 2758

Quoted 7 lines

kernel/trace/bpf_trace.c +4 -0

@@ -2752,6 +2752,10 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
        if (!is_kprobe_multi(prog))
                return -EINVAL;
 
+       /* kprobe_multi is not allowed to be sleepable. */
+       if (prog->sleepable)
+               return -EINVAL;
+

Looks ok to me, Jiri, could you also take a look?

Quoted 6 lines

kernel/trace/bpf_trace.c +0 -1

        /* Writing to context is not allowed for kprobes. */
        if (prog->aux->kprobe_write_ctx)
                return -EINVAL;
--

2.53.0

Kumar Kartikeya Dwivedi

maintainer

2026-04-01 14:43 UTC #3 lore raw

Re: [PATCH bpf] bpf: Reject sleepable kprobe_multi programs at attach time

Quoted 41 lines · Kumar Kartikeya Dwivedi

Quoted 14 lines · Varun R Mallya
kprobe.multi programs run in atomic/RCU context and cannot sleep. However, bpf_kprobe_multi_link_attach() did not validate whether the program being attached had the sleepable flag set, allowing sleepable helpers such as bpf_copy_from_user() to be invoked from a non-sleepable context.
This causes a "sleeping function called from invalid context" splat:
  BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:169
  in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1787, name: sudo
  preempt_count: 1, expected: 0
  RCU nest depth: 2, expected: 0
Quoted 4 lines
Fix this by rejecting sleepable programs early in bpf_kprobe_multi_link_attach(), before any further processing.
Fixes 0dcac272540613d41c05e89679e4ddb978b612f1 ("bpf: Add multi kprobe link")
Please use the right format.
Fixes 0dcac2725406 ("bpf: Add multi kprobe link")
You can add the follow to your .gitconfig to generate the fixes tag. [alias]
    fixes = log -1 --format='Fixes: %h (\"%s\")'
Quoted 13 lines
Signed-off-by Varun R Mallya <[email protected]>
---
 kernel/trace/bpf_trace.c | 4 ++++
 1 file changed, 4 insertions(+)
kernel/trace/bpf_trace.c +0 -0
index 0b040a417442..af7079aa0f36 100644
@@ -2752,6 +2752,10 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
        if (!is_kprobe_multi(prog))
                return -EINVAL;
 

Quoted 13 lines

kernel/trace/bpf_trace.c int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr · line 2758
Quoted 4 lines
kernel/trace/bpf_trace.c +4 -0
+       /* kprobe_multi is not allowed to be sleepable. */
+       if (prog->sleepable)
+               return -EINVAL;
+
Looks ok to me, Jiri, could you also take a look?
Quoted 6 lines
kernel/trace/bpf_trace.c +0 -1
        /* Writing to context is not allowed for kprobes. */
        if (prog->aux->kprobe_write_ctx)
                return -EINVAL;
--
2.53.0

Also, please add a selftest.

pw-bot: cr

Varun R Mallya

author

2026-04-01 16:26 UTC #4 lore raw

PATCH v2 1/1 bpf: Reject sleepable kprobe_multi programs at attach time

In reply to Varun R Mallya

This causes a "sleeping function called from invalid context" splat:

  BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:169
  in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1787, name: sudo
  preempt_count: 1, expected: 0
  RCU nest depth: 2, expected: 0

Fix this by rejecting sleepable programs early in bpf_kprobe_multi_link_attach(), before any further processing.

Also add a selftest that tries to load a sleepable kprobe_multi program and it needs to be rejected for the test to pass.

Fixes 0dcac2725406 ("bpf: Add multi kprobe link")

Signed-off-by Varun R Mallya <[email protected]>

---
 kernel/trace/bpf_trace.c                      |  4 ++
 .../bpf/prog_tests/kprobe_multi_test.c        | 41 +++++++++++++++++++
 .../bpf/progs/kprobe_multi_sleepable.c        | 13 ++++++
 3 files changed, 58 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c

kernel/trace/bpf_trace.c +4 -0

index 0b040a417442..af7079aa0f36 100644
@@ -2752,6 +2752,10 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	if (!is_kprobe_multi(prog))
 		return -EINVAL;
 
+	/* kprobe_multi is not allowed to be sleepable. */
+	if (prog->sleepable)
+		return -EINVAL;
+
 	/* Writing to context is not allowed for kprobes. */
 	if (prog->aux->kprobe_write_ctx)
 		return -EINVAL;

tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c +41 -0

58 lines not on this page · raw message

tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c new file +13 -0

new file mode 100644
index 000000000000..56973ad8779d
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+SEC("kprobe.multi")
+int handle_kprobe_multi_sleepable(struct pt_regs *ctx)
+{
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";

Signature · 1 line

2.53.0

Kumar Kartikeya Dwivedi

maintainer

2026-04-01 16:31 UTC #5 lore raw

Re: [PATCH bpf v2] bpf: Reject sleepable kprobe_multi programs at attach time

Quoted 17 lines · Varun R Mallya

kprobe.multi programs run in atomic/RCU context and cannot sleep. However, bpf_kprobe_multi_link_attach() did not validate whether the program being attached had the sleepable flag set, allowing sleepable helpers such as bpf_copy_from_user() to be invoked from a non-sleepable context.
This causes a "sleeping function called from invalid context" splat:
  BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:169
  in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1787, name: sudo
  preempt_count: 1, expected: 0
  RCU nest depth: 2, expected: 0
Fix this by rejecting sleepable programs early in bpf_kprobe_multi_link_attach(), before any further processing.

Quoted 6 lines

Also add a selftest that tries to load a sleepable kprobe_multi program and it needs to be rejected for the test to pass.
Fixes 0dcac2725406 ("bpf: Add multi kprobe link")
Signed-off-by Varun R Mallya <[email protected]>
---

Looks ok, but please split kernel fix and tests into separate patches, and no need to reply to this thread.

pw-bot: cr

Quoted 108 lines

 kernel/trace/bpf_trace.c                      |  4 ++
 .../bpf/prog_tests/kprobe_multi_test.c        | 41 +++++++++++++++++++
 .../bpf/progs/kprobe_multi_sleepable.c        | 13 ++++++
 3 files changed, 58 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c

kernel/trace/bpf_trace.c +4 -0

index 0b040a417442..af7079aa0f36 100644
@@ -2752,6 +2752,10 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
        if (!is_kprobe_multi(prog))
                return -EINVAL;
 
+       /* kprobe_multi is not allowed to be sleepable. */
+       if (prog->sleepable)
+               return -EINVAL;
+
        /* Writing to context is not allowed for kprobes. */
        if (prog->aux->kprobe_write_ctx)
                return -EINVAL;

tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c +41 -0

index 78c974d4ea33..f02fec2b6fda 100644
@@ -10,6 +10,7 @@
 #include "kprobe_multi_session_cookie.skel.h"
 #include "kprobe_multi_verifier.skel.h"
 #include "kprobe_write_ctx.skel.h"
+#include "kprobe_multi_sleepable.skel.h"
 #include "bpf/libbpf_internal.h"
 #include "bpf/hashmap.h"

@@ -633,6 +634,44 @@ static void test_attach_write_ctx(void)
 }
 #endif
 
+static void test_attach_multi_sleepable(void)
+{
+       struct kprobe_multi_sleepable *skel;
+       int err;
+
+       skel = kprobe_multi_sleepable__open();
+       if (!ASSERT_OK_PTR(skel, "kprobe_multi_sleepable__open"))
+               return;
+
+       err = bpf_program__set_flags(skel->progs.handle_kprobe_multi_sleepable,
+                                    BPF_F_SLEEPABLE);
+       if (!ASSERT_OK(err, "bpf_program__set_flags"))
+               goto cleanup;
+
+       /* Load should succeed even with BPF_F_SLEEPABLE for KPROBE types */
+       err = kprobe_multi_sleepable__load(skel);
+       if (!ASSERT_OK(err, "kprobe_multi_sleepable__load"))
+               goto cleanup;
+
+       /* Attachment must fail for kprobe.multi + BPF_F_SLEEPABLE.
+        * Also chosen a stable symbol to send into opts
+        */
+       LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
+       const char *sym = "vfs_read";
+
+       opts.syms = &sym;
+       opts.cnt = 1;
+
+       skel->links.handle_kprobe_multi_sleepable =
+               bpf_program__attach_kprobe_multi_opts(skel->progs.handle_kprobe_multi_sleepable,
+                                                     NULL, &opts);
+       ASSERT_ERR_PTR(skel->links.handle_kprobe_multi_sleepable,
+                      "bpf_program__attach_kprobe_multi_opts");
+
+cleanup:
+       kprobe_multi_sleepable__destroy(skel);
+}
+
 void serial_test_kprobe_multi_bench_attach(void)
 {
        if (test__start_subtest("kernel"))

@@ -676,5 +715,7 @@ void test_kprobe_multi_test(void)
                test_unique_match();
        if (test__start_subtest("attach_write_ctx"))
                test_attach_write_ctx();
+       if (test__start_subtest("attach_multi_sleepable"))
+               test_attach_multi_sleepable();
        RUN_TESTS(kprobe_multi_verifier);
 }

tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c new file +13 -1

new file mode 100644
index 000000000000..56973ad8779d
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+SEC("kprobe.multi")
+int handle_kprobe_multi_sleepable(struct pt_regs *ctx)
+{
+       return 0;
+}
+
+char _license[] SEC("license") = "GPL";
--

2.53.0