* [PATCH] Log if a core dump is aborted due to changed file permissions
@ 2021-07-01 23:31 David Oberhollenzer
2021-08-02 20:47 ` David Oberhollenzer
2021-08-02 21:40 ` Andrew Morton
0 siblings, 2 replies; 3+ messages in thread
From: David Oberhollenzer @ 2021-07-01 23:31 UTC (permalink / raw)
To: viro, linux-fsdevel, linux-kernel; +Cc: richard, David Oberhollenzer
For obvious security reasons, a core dump is aborted if the
filesystem cannot preserve ownership or permissions of the
dump file.
This affects filesystems like e.g. vfat, but also something like
a 9pfs share in a Qemu test setup, running as a regular user,
depending on the security model used. In those cases, the result
is an empty core file and a confused user.
To hopefully safe other people a lot of time figuring out the
cause, this patch adds a simple log message for those specific
cases.
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>
---
fs/coredump.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/fs/coredump.c b/fs/coredump.c
index c3d8fc14b993..3e53d3e18b0e 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -782,10 +777,17 @@ void do_coredump(const kernel_siginfo_t *siginfo)
* filesystem.
*/
mnt_userns = file_mnt_user_ns(cprm.file);
- if (!uid_eq(i_uid_into_mnt(mnt_userns, inode), current_fsuid()))
+ if (!uid_eq(i_uid_into_mnt(mnt_userns, inode),
+ current_fsuid())) {
+ pr_info_ratelimited("Core dump to |%s aborted: cannot preserve file owner\n",
+ cn.corename);
goto close_fail;
- if ((inode->i_mode & 0677) != 0600)
+ }
+ if ((inode->i_mode & 0677) != 0600) {
+ pr_info_ratelimited("Core dump to |%s aborted: cannot preserve file permissions\n",
+ cn.corename);
goto close_fail;
+ }
if (!(cprm.file->f_mode & FMODE_CAN_WRITE))
goto close_fail;
if (do_truncate(mnt_userns, cprm.file->f_path.dentry,
--
2.31.1
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] Log if a core dump is aborted due to changed file permissions
2021-07-01 23:31 [PATCH] Log if a core dump is aborted due to changed file permissions David Oberhollenzer
@ 2021-08-02 20:47 ` David Oberhollenzer
2021-08-02 21:40 ` Andrew Morton
1 sibling, 0 replies; 3+ messages in thread
From: David Oberhollenzer @ 2021-08-02 20:47 UTC (permalink / raw)
To: viro, linux-fsdevel, linux-kernel; +Cc: richard, Andrew Morton
Friendly ping :-)
On 7/2/21 1:31 AM, David Oberhollenzer wrote:
> For obvious security reasons, a core dump is aborted if the
> filesystem cannot preserve ownership or permissions of the
> dump file.
>
> This affects filesystems like e.g. vfat, but also something like
> a 9pfs share in a Qemu test setup, running as a regular user,
> depending on the security model used. In those cases, the result
> is an empty core file and a confused user.
>
> To hopefully safe other people a lot of time figuring out the
> cause, this patch adds a simple log message for those specific
> cases.
>
> Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>
> ---
> fs/coredump.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/fs/coredump.c b/fs/coredump.c
> index c3d8fc14b993..3e53d3e18b0e 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -782,10 +777,17 @@ void do_coredump(const kernel_siginfo_t *siginfo)
> * filesystem.
> */
> mnt_userns = file_mnt_user_ns(cprm.file);
> - if (!uid_eq(i_uid_into_mnt(mnt_userns, inode), current_fsuid()))
> + if (!uid_eq(i_uid_into_mnt(mnt_userns, inode),
> + current_fsuid())) {
> + pr_info_ratelimited("Core dump to |%s aborted: cannot preserve file owner\n",
> + cn.corename);
> goto close_fail;
> - if ((inode->i_mode & 0677) != 0600)
> + }
> + if ((inode->i_mode & 0677) != 0600) {
> + pr_info_ratelimited("Core dump to |%s aborted: cannot preserve file permissions\n",
> + cn.corename);
> goto close_fail;
> + }
> if (!(cprm.file->f_mode & FMODE_CAN_WRITE))
> goto close_fail;
> if (do_truncate(mnt_userns, cprm.file->f_path.dentry,
> --
> 2.31.1
>
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] Log if a core dump is aborted due to changed file permissions
2021-07-01 23:31 [PATCH] Log if a core dump is aborted due to changed file permissions David Oberhollenzer
2021-08-02 20:47 ` David Oberhollenzer
@ 2021-08-02 21:40 ` Andrew Morton
1 sibling, 0 replies; 3+ messages in thread
From: Andrew Morton @ 2021-08-02 21:40 UTC (permalink / raw)
To: David Oberhollenzer; +Cc: viro, linux-fsdevel, linux-kernel, richard
On Fri, 2 Jul 2021 01:31:51 +0200 David Oberhollenzer <david.oberhollenzer@sigma-star.at> wrote:
> For obvious security reasons, a core dump is aborted if the
> filesystem cannot preserve ownership or permissions of the
> dump file.
>
> This affects filesystems like e.g. vfat, but also something like
> a 9pfs share in a Qemu test setup, running as a regular user,
> depending on the security model used. In those cases, the result
> is an empty core file and a confused user.
>
> To hopefully safe other people a lot of time figuring out the
> cause, this patch adds a simple log message for those specific
> cases.
Seems sane.
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -782,10 +777,17 @@ void do_coredump(const kernel_siginfo_t *siginfo)
> * filesystem.
> */
> mnt_userns = file_mnt_user_ns(cprm.file);
> - if (!uid_eq(i_uid_into_mnt(mnt_userns, inode), current_fsuid()))
> + if (!uid_eq(i_uid_into_mnt(mnt_userns, inode),
> + current_fsuid())) {
> + pr_info_ratelimited("Core dump to |%s aborted: cannot preserve file owner\n",
But why the "|%s"? This signifies dump-to-pipe, yes? Don't we need
the below?
--- a/fs/coredump.c~log-if-a-core-dump-is-aborted-due-to-changed-file-permissions-fix
+++ a/fs/coredump.c
@@ -784,12 +784,12 @@ void do_coredump(const kernel_siginfo_t
mnt_userns = file_mnt_user_ns(cprm.file);
if (!uid_eq(i_uid_into_mnt(mnt_userns, inode),
current_fsuid())) {
- pr_info_ratelimited("Core dump to |%s aborted: cannot preserve file owner\n",
+ pr_info_ratelimited("Core dump to %s aborted: cannot preserve file owner\n",
cn.corename);
goto close_fail;
}
if ((inode->i_mode & 0677) != 0600) {
- pr_info_ratelimited("Core dump to |%s aborted: cannot preserve file permissions\n",
+ pr_info_ratelimited("Core dump to %s aborted: cannot preserve file permissions\n",
cn.corename);
goto close_fail;
}
_
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-07-01 23:31 [PATCH] Log if a core dump is aborted due to changed file permissions David Oberhollenzer
2021-08-02 20:47 ` David Oberhollenzer
2021-08-02 21:40 ` Andrew Morton
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