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man/man2const/F_{ADD,GET}_SEALS.2const: document F_SEAL_EXEC

PATCH In review Pratyush Yadav 2 participants 2 messages May 29 – Jun 1

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Memory management Man-pages: manual pages for Linux -- Sections 2, 3, 4, 5, and 7
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Pratyush Yadav

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PATCH v2 1/1 man/man2const/F_{ADD,GET}_SEALS.2const: document F_SEAL_EXEC

From: "Pratyush Yadav (Google)" <[email protected]>

F_SEAL_EXEC was added in Linux v6.3. It blocks changing of the exec bits once added. Document it.

Signed-off-by Pratyush Yadav (Google) <[email protected]>

---

Notes:
I discovered this was missing when working on [0]. I had to look at the code to figure out how it was supposed to behave.

Changes in v2:
- Re-write the documentation by hand.

[0] https://lore.kernel.org/linux-mm/[email protected]/

 man/man2const/F_GET_SEALS.2const | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
man/man2const/F_GET_SEALS.2const +19 -0
index 175025c10..f41e1748a 100644
@@ -176,6 +176,25 @@ will fail with
 Using this seal,
 one process can create a memory buffer that it can continue to modify
 while sharing that buffer on a "read-only" basis with other processes.
+.TP
+.BR F_SEAL_EXEC " (since Linux 6.3)"
+If this seal is set, the execute mode bits of the file cannot be modified.
+Attempting to change the execute mode bits via
+.BR fchmod (2)
+or similar will fail with
+.BR EPERM .
+This results in a memfd that is either permanently executable or
+permanently un-executable.
+.IP
+Adding this seal implicitly adds
+.BR F_SEAL_GROW ,
+.BR F_SEAL_SHRINK ,
+.BR F_SEAL_WRITE ,
+and
+.BR F_SEAL_FUTURE_WRITE .
+This ensures that the executable code is not writeable.
+All the pre-requisites to add the implied seals must be met to successfully add
+.BR F_SEAL_EXEC .
 .SH RETURN VALUE
 .TP
 .B F_GET_SEALS

base-commit: 9db8ca91f920b9aba40ed68de6b8da0ca9dbefaa

Signature · 1 line
2.54.0.1013.g208068f2d8-goog
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#1 lore raw

Hi Pratyush,

Quoted 8 lines · Pratyush Yadav

From: "Pratyush Yadav (Google)" <[email protected]>

F_SEAL_EXEC was added in Linux v6.3. It blocks changing of the exec bits once added. Document it.

Signed-off-by Pratyush Yadav (Google) <[email protected]>

---

Quoted 8 lines

Notes:
I discovered this was missing when working on [0]. I had to look at the code to figure out how it was supposed to behave.

Changes in v2:
- Re-write the documentation by hand.

[0] https://lore.kernel.org/linux-mm/[email protected]/

Thanks! I've applied the patch, with a few minor tweaks:

diff --git i/man/man2const/F_GET_SEALS.2const w/man/man2const/F_GET_SEALS.2const index f41e1748acd0..686a92fddefe 100644
--- i/man/man2const/F_GET_SEALS.2const
+++ w/man/man2const/F_GET_SEALS.2const
@@ -178,13 +178,15 @@ .SH DESCRIPTION
while sharing that buffer on a "read-only" basis with other processes. .TP
.BR F_SEAL_EXEC " (since Linux 6.3)"
-If this seal is set, the execute mode bits of the file cannot be modified. +If this seal is set,
+the execute mode bits of the file cannot be modified.
Attempting to change the execute mode bits via
.BR fchmod (2)
or similar will fail with
.BR EPERM .
-This results in a memfd that is either permanently executable or -permanently un-executable.
+This results in a memfd that is
+either permanently executable
+or permanently not executable.
.IP
Adding this seal implicitly adds
.BR F_SEAL_GROW ,
@@ -193,7 +195,8 @@ .SH DESCRIPTION
and
.BR F_SEAL_FUTURE_WRITE .
This ensures that the executable code is not writeable.
-All the pre-requisites to add the implied seals must be met to successfully add +All the pre-requisites to add the implied seals must be met
+to successfully add
.BR F_SEAL_EXEC .
.SH RETURN VALUE
.TP

Have a lovely night!
Alex

Quoted 40 lines
 man/man2const/F_GET_SEALS.2const | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
man/man2const/F_GET_SEALS.2const +19 -0
index 175025c10..f41e1748a 100644
@@ -176,6 +176,25 @@ will fail with
 Using this seal,
 one process can create a memory buffer that it can continue to modify
 while sharing that buffer on a "read-only" basis with other processes.
+.TP
+.BR F_SEAL_EXEC " (since Linux 6.3)"
+If this seal is set, the execute mode bits of the file cannot be modified.
+Attempting to change the execute mode bits via
+.BR fchmod (2)
+or similar will fail with
+.BR EPERM .
+This results in a memfd that is either permanently executable or
+permanently un-executable.
+.IP
+Adding this seal implicitly adds
+.BR F_SEAL_GROW ,
+.BR F_SEAL_SHRINK ,
+.BR F_SEAL_WRITE ,
+and
+.BR F_SEAL_FUTURE_WRITE .
+This ensures that the executable code is not writeable.
+All the pre-requisites to add the implied seals must be met to successfully add
+.BR F_SEAL_EXEC .
 .SH RETURN VALUE
 .TP
 .B F_GET_SEALS

base-commit: 9db8ca91f920b9aba40ed68de6b8da0ca9dbefaa

Signature · 1 line
2.54.0.1013.g208068f2d8-goog
Signature · 1 line
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