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Fix exec_imgact_shell()'s handling of two error cases: (1) Previously, if

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the first line of a script exceeded MAXSHELLCMDLEN characters, then
exec_imgact_shell() silently truncated the line and passed on the truncated
interpreter name or argument.  Now, exec_imgact_shell() will fail and return
ENOEXEC, which is the commonly used errno among Unix variants for this type
of error. (2) Previously, exec_imgact_shell()'s check on the length of the
interpreter's name was ineffective.  In other words, exec_imgact_shell()
could not possibly fail and return ENAMETOOLONG.  The reason being that the
length of the interpreter name had to exceed MAXSHELLCMDLEN characters in
order that ENAMETOOLONG be returned.  But, the search for the end of the
interpreter name stops after at most MAXSHELLCMDLEN - 2 characters are
scanned.  (In the end, this particular error is eventually discovered
outside of exec_imgact_shell() and ENAMETOOLONG is returned.  So, the real
effect of this second change is that the error is detected earlier, in
exec_imgact_shell().)

Update the definition of MAXINTERP to the actual limit on the size of
the interpreter name that has been in effect since r142453 (from
2005).

In collaboration with: kib
This commit is contained in:
Alan Cox 2010-09-21 16:24:51 +00:00
parent 088acbb312
commit 8f7f5a7f26
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=212965
3 changed files with 23 additions and 17 deletions
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10
lib/libc/sys/execve.2
View File

@ -28,7 +28,7 @@
.\" @(#)execve.2 8.5 (Berkeley) 6/1/94
.\" $FreeBSD$
.\"
.Dd April 10, 2008
.Dd September 21, 2010
.Dt EXECVE 2
.Os
.Sh NAME
@ -256,9 +256,11 @@ A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.It Bq Er ENAMETOOLONG
When invoking an interpreted script, the interpreter name
exceeds
.It Bq Er ENOEXEC
When invoking an interpreted script, the length of the first line,
inclusive of the
.Sy \&#!
prefix and terminating newline, exceeds
.Dv MAXSHELLCMDLEN
characters.
.It Bq Er ENOENT

28
sys/kern/imgact_shell.c
View File

@ -46,13 +46,18 @@ __FBSDID("$FreeBSD$");
/*
* At the time of this writing, MAXSHELLCMDLEN == PAGE_SIZE. This is
* significant because the caller has only mapped in one page of the
* file we're reading. This code should be changed to know how to
* read in the second page, but I'm not doing that just yet...
* file we're reading.
*/
#if MAXSHELLCMDLEN > PAGE_SIZE
#error "MAXSHELLCMDLEN is larger than a single page!"
#endif
/*
* MAXSHELLCMDLEN must be at least MAXINTERP plus the size of the `#!'
* prefix and terminating newline.
*/
CTASSERT(MAXSHELLCMDLEN >= MAXINTERP + 3);
/**
* Shell interpreter image activator. An interpreter name beginning at
* imgp->args->begin_argv is the minimal successful exit requirement.
@ -98,20 +103,20 @@ exec_shell_imgact(imgp)
const char *image_header = imgp->image_header;
const char *ihp, *interpb, *interpe, *maxp, *optb, *opte, *fname;
int error, offset;
size_t length, clength;
size_t length;
struct vattr vattr;
struct sbuf *sname;
/* a shell script? */
if (((const short *) image_header)[0] != SHELLMAGIC)
return(-1);
if (((const short *)image_header)[0] != SHELLMAGIC)
return (-1);
/*
* Don't allow a shell script to be the shell for a shell
* script. :-)
*/
if (imgp->interpreted)
return(ENOEXEC);
return (ENOEXEC);
imgp->interpreted = 1;
@ -127,12 +132,9 @@ exec_shell_imgact(imgp)
/*
* Copy shell name and arguments from image_header into a string
* buffer. Remember that the caller has mapped only the
* first page of the file into memory.
* buffer.
*/
clength = (vattr.va_size > PAGE_SIZE) ? PAGE_SIZE : vattr.va_size;
maxp = &image_header[clength];
maxp = &image_header[MIN(vattr.va_size, MAXSHELLCMDLEN)];
ihp = &image_header[2];
/*
@ -149,7 +151,7 @@ exec_shell_imgact(imgp)
interpe = ihp;
if (interpb == interpe)
return (ENOEXEC);
if ((interpe - interpb) >= MAXSHELLCMDLEN)
if (interpe - interpb >= MAXINTERP)
return (ENAMETOOLONG);
/*
@ -163,6 +165,8 @@ exec_shell_imgact(imgp)
while (ihp < maxp && ((*ihp != '\n') && (*ihp != '\0')))
ihp++;
opte = ihp;
if (opte == maxp)
return (ENOEXEC);
while (--ihp > optb && ((*ihp == ' ') || (*ihp == '\t')))
opte = ihp;

2
sys/sys/param.h
View File

@ -73,7 +73,7 @@
#include <sys/syslimits.h>
#define MAXCOMLEN 19 /* max command name remembered */
#define MAXINTERP 32 /* max interpreter file name length */
#define MAXINTERP PATH_MAX /* max interpreter file name length */
#define MAXLOGNAME 17 /* max login name length (incl. NUL) */
#define MAXUPRC CHILD_MAX /* max simultaneous processes */
#define NCARGS ARG_MAX /* max bytes for an exec function */