svn commit: r367942 - head/sys/kern
Kyle Evans
kevans at FreeBSD.org
Mon Nov 23 00:33:07 UTC 2020
Author: kevans
Date: Mon Nov 23 00:33:06 2020
New Revision: 367942
URL: https://svnweb.freebsd.org/changeset/base/367942
Log:
kern: dup: do not assume oldfde is valid
oldfde may be invalidated if the table has grown due to the operation that
we're performing, either via fdalloc() or a direct fdgrowtable_exp().
This was technically OK before rS367927 because the old table remained valid
until the filedesc became unused, but now it may be freed immediately if
it's an unshared table in a single-threaded process, so it is no longer a
good assumption to make.
This fixes dup/dup2 invocations that grow the file table; in the initial
report, it manifested as a kernel panic in devel/gmake's configure script.
Reported by: Guy Yur <guyyur gmail com>
Reviewed by: rew
Differential Revision: https://reviews.freebsd.org/D27319
Modified:
head/sys/kern/kern_descrip.c
Modified: head/sys/kern/kern_descrip.c
==============================================================================
--- head/sys/kern/kern_descrip.c Sun Nov 22 20:21:10 2020 (r367941)
+++ head/sys/kern/kern_descrip.c Mon Nov 23 00:33:06 2020 (r367942)
@@ -870,7 +870,7 @@ kern_dup(struct thread *td, u_int mode, int flags, int
struct filedesc *fdp;
struct filedescent *oldfde, *newfde;
struct proc *p;
- struct file *delfp;
+ struct file *delfp, *oldfp;
u_long *oioctls, *nioctls;
int error, maxfd;
@@ -910,7 +910,8 @@ kern_dup(struct thread *td, u_int mode, int flags, int
}
oldfde = &fdp->fd_ofiles[old];
- if (!fhold(oldfde->fde_file))
+ oldfp = oldfde->fde_file;
+ if (!fhold(oldfp))
goto unlock;
/*
@@ -922,14 +923,14 @@ kern_dup(struct thread *td, u_int mode, int flags, int
case FDDUP_NORMAL:
case FDDUP_FCNTL:
if ((error = fdalloc(td, new, &new)) != 0) {
- fdrop(oldfde->fde_file, td);
+ fdrop(oldfp, td);
goto unlock;
}
break;
case FDDUP_MUSTREPLACE:
/* Target file descriptor must exist. */
if (fget_locked(fdp, new) == NULL) {
- fdrop(oldfde->fde_file, td);
+ fdrop(oldfp, td);
goto unlock;
}
break;
@@ -948,7 +949,7 @@ kern_dup(struct thread *td, u_int mode, int flags, int
error = racct_set_unlocked(p, RACCT_NOFILE, new + 1);
if (error != 0) {
error = EMFILE;
- fdrop(oldfde->fde_file, td);
+ fdrop(oldfp, td);
goto unlock;
}
}
@@ -963,6 +964,12 @@ kern_dup(struct thread *td, u_int mode, int flags, int
}
KASSERT(old != new, ("new fd is same as old"));
+
+ /* Refetch oldfde because the table may have grown and old one freed. */
+ oldfde = &fdp->fd_ofiles[old];
+ KASSERT(oldfp == oldfde->fde_file,
+ ("fdt_ofiles shift from growth observed at fd %d",
+ old));
newfde = &fdp->fd_ofiles[new];
delfp = newfde->fde_file;
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