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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Orit Wasserman <orit.was@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@redhat.com>,
	Elazar Leibovich <elazar@lightbitslabs.com>,
	"Steven Rostedt (VMware)" <rostedt@goodmis.org>
Subject: [PATCH 4.9 24/53] tracing: Fix partial reading of trace events id file
Date: Thu, 23 May 2019 21:05:48 +0200	[thread overview]
Message-ID: <20190523181714.682253388@linuxfoundation.org> (raw)
In-Reply-To: <20190523181710.981455400@linuxfoundation.org>

From: Elazar Leibovich <elazar@lightbitslabs.com>

commit cbe08bcbbe787315c425dde284dcb715cfbf3f39 upstream.

When reading only part of the id file, the ppos isn't tracked correctly.
This is taken care by simple_read_from_buffer.

Reading a single byte, and then the next byte would result EOF.

While this seems like not a big deal, this breaks abstractions that
reads information from files unbuffered. See for example
https://github.com/golang/go/issues/29399

This code was mentioned as problematic in
commit cd458ba9d5a5
("tracing: Do not (ab)use trace_seq in event_id_read()")

An example C code that show this bug is:

  #include <stdio.h>
  #include <stdint.h>

  #include <sys/types.h>
  #include <sys/stat.h>
  #include <fcntl.h>
  #include <unistd.h>

  int main(int argc, char **argv) {
    if (argc < 2)
      return 1;
    int fd = open(argv[1], O_RDONLY);
    char c;
    read(fd, &c, 1);
    printf("First  %c\n", c);
    read(fd, &c, 1);
    printf("Second %c\n", c);
  }

Then run with, e.g.

  sudo ./a.out /sys/kernel/debug/tracing/events/tcp/tcp_set_state/id

You'll notice you're getting the first character twice, instead of the
first two characters in the id file.

Link: http://lkml.kernel.org/r/20181231115837.4932-1-elazar@lightbitslabs.com

Cc: Orit Wasserman <orit.was@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 23725aeeab10b ("ftrace: provide an id file for each event")
Signed-off-by: Elazar Leibovich <elazar@lightbitslabs.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/trace/trace_events.c |    3 ---
 1 file changed, 3 deletions(-)

--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1310,9 +1310,6 @@ event_id_read(struct file *filp, char __
 	char buf[32];
 	int len;
 
-	if (*ppos)
-		return 0;
-
 	if (unlikely(!id))
 		return -ENODEV;
 



  parent reply	other threads:[~2019-05-23 19:09 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-23 19:05 [PATCH 4.9 00/53] 4.9.179-stable review Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 01/53] net: avoid weird emergency message Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 02/53] net/mlx4_core: Change the error print to info print Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 03/53] ppp: deflate: Fix possible crash in deflate_init Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 04/53] tipc: switch order of device registration to fix a crash Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 05/53] vsock/virtio: free packets during the socket release Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 06/53] tipc: fix modprobe tipc failed after switch order of device registration Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 07/53] vsock/virtio: Initialize core virtio vsock before registering the driver Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 08/53] parisc: Export running_on_qemu symbol for modules Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 09/53] parisc: Skip registering LED when running in QEMU Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 10/53] parisc: Rename LEVEL to PA_ASM_LEVEL to avoid name clash with DRBD code Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 11/53] stm class: Fix channel free in stm output free path Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 12/53] md: add mddev->pers to avoid potential NULL pointer dereference Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 13/53] intel_th: msu: Fix single mode with IOMMU Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 14/53] p54: drop device reference count if fails to enable device Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 15/53] of: fix clang -Wunsequenced for be32_to_cpu() Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 16/53] cifs: fix strcat buffer overflow and reduce raciness in smb21_set_oplock_level() Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 17/53] media: ov6650: Fix sensor possibly not detected on probe Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 18/53] NFS4: Fix v4.0 client state corruption when mount Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 19/53] clk: tegra: Fix PLLM programming on Tegra124+ when PMC overrides divider Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 20/53] fuse: fix writepages on 32bit Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 21/53] fuse: honor RLIMIT_FSIZE in fuse_file_fallocate Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 22/53] iommu/tegra-smmu: Fix invalid ASID bits on Tegra30/114 Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 23/53] ceph: flush dirty inodes before proceeding with remount Greg Kroah-Hartman
2019-05-23 19:05 ` Greg Kroah-Hartman [this message]
2019-05-23 19:05 ` [PATCH 4.9 25/53] memory: tegra: Fix integer overflow on tick value calculation Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 26/53] perf intel-pt: Fix instructions sampling rate Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 27/53] perf intel-pt: Fix improved sample timestamp Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 28/53] perf intel-pt: Fix sample timestamp wrt non-taken branches Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 29/53] objtool: Allow AR to be overridden with HOSTAR Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 30/53] fbdev: sm712fb: fix brightness control on reboot, dont set SR30 Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 31/53] fbdev: sm712fb: fix VRAM detection, dont set SR70/71/74/75 Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 32/53] fbdev: sm712fb: fix white screen of death on reboot, dont set CR3B-CR3F Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 33/53] fbdev: sm712fb: fix boot screen glitch when sm712fb replaces VGA Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 34/53] fbdev: sm712fb: fix crashes during framebuffer writes by correctly mapping VRAM Greg Kroah-Hartman
2019-05-23 19:05 ` [PATCH 4.9 35/53] fbdev: sm712fb: fix support for 1024x768-16 mode Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 36/53] fbdev: sm712fb: use 1024x768 by default on non-MIPS, fix garbled display Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 37/53] fbdev: sm712fb: fix crashes and garbled display during DPMS modesetting Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 38/53] PCI: Mark Atheros AR9462 to avoid bus reset Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 39/53] PCI: Factor out pcie_retrain_link() function Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 40/53] PCI: Work around Pericom PCIe-to-PCI bridge Retrain Link erratum Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 41/53] dm delay: fix a crash when invalid device is specified Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 42/53] xfrm: policy: Fix out-of-bound array accesses in __xfrm_policy_unlink Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 43/53] xfrm6_tunnel: Fix potential panic when unloading xfrm6_tunnel module Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 44/53] vti4: ipip tunnel deregistration fixes Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 45/53] xfrm4: Fix uninitialized memory read in _decode_session4 Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 46/53] mac80211: Fix kernel panic due to use of txq after free Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 47/53] KVM: arm/arm64: Ensure vcpu target is unset on reset failure Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 48/53] power: supply: sysfs: prevent endless uevent loop with CONFIG_POWER_SUPPLY_DEBUG Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 49/53] ufs: fix braino in ufs_get_inode_gid() for solaris UFS flavour Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 50/53] perf bench numa: Add define for RUSAGE_THREAD if not present Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 51/53] Revert "Dont jump to compute_result state from check_result state" Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 52/53] md/raid: raid5 preserve the writeback action after the parity check Greg Kroah-Hartman
2019-05-23 19:06 ` [PATCH 4.9 53/53] btrfs: Honour FITRIM range constraints during free space trim Greg Kroah-Hartman
2019-05-24  5:28 ` [PATCH 4.9 00/53] 4.9.179-stable review kernelci.org bot
2019-05-24  8:43 ` Naresh Kamboju
2019-05-24 11:04 ` Jon Hunter
2019-05-24 18:56 ` shuah

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